Never said Stefanski isn't a decent coach. He's a very good OC, but not a great head coach imo. Heck, with some of the news about Saban and Cleveland today Snake's theory of Stefanski's time unemployed might get tested (I think it'd likely be quick but most likely get hired as an OC somewhere). That being said, you've implied before that Mayfield was the reason he'd had so many coaches over the seasons. But we'll let that slide, read carefully and you might learn something.
One of the key things that people like you gloss over in the 'many different coaches' discussion about players (not just Mayfield btw), is the systems they are in and how different they are from one another not necessarily the tweaks the coach's make to that system. In Mayfield's first three seasons, he had three different basic offensive systems. For the sake of this discussion we'll focus on 2019 and 2020 to help you understand why the Browns' record and offense improved - Stefanski helped, but more so Mayfield was finally in a system that fits his skillset best. This will be important later as it relates to his time here. You can refer back to the post you quoted for the three basic systems.
In 2019, the Browns ran a version of the Air Coryell offense, which is what the Bucs also had under Arians and Brady. High risk, high reward with the passing game emphasizing big plays. QBs in their first years in the Air Coryell offense tend to throw a lot of INTS. See Winston and Mayfield's 2019 seasons as prime examples. Heck, can throw in Brady's 2020 as well, he was over his average yearly INT total in 2020 with 12 or tied for his 3rd worst season (he's got a could of 14s, a 13 and then a lot of 12's - two with the Bucs). As Arians said, "No risk it, no biscuit'. The Browns in 2019 had a lot of troubles on their o-line and offense in general. Only 2 o-line played every game (LG and C), revolving doors at tackle (literally and figuratively) and despite having OBJ their best receiver was Jarvis Landry. OBJ was on the injured report every week of the 2019 season and was showing the effects of the multiple ankle injuries he'd had in the past couple of seasons. Lowest catch rate of his career to that point at 53%. So, they were snakebit on offense kinda like we were on defense last year. Just lots of injuries and guys missing games. Not idea - especially on the o-line - when trying to get a new offense installed.
Now, as we know from watching Arians' version here in Tampa, the Air Coryell offense is pass-heavy - especially wanting to throw deep. Freddie Kitchens in his infinite wisdom decided they were going to emphasize the run so much so that in one of the 4 one score games they lost after having a lead he decided to call a draw play on 4th and 9 against the Ravens. It went about as well as you can expect. Play distribution was still pass-heavy but a good bit less than what most Air Coryell offenses run (56-44 for the Browns, typically more like 60-40 like what the Bucs had with a 61-39 ratio in 2020).
Mayfield played behind a porous o-line, had 21 interceptions but was rated to have less bad throws than Aaron Rodgers and Tom Brady in that season. He ranked 14th in bad throw percentage. So, in 2019 in his second season he had a really bad offensive line with almost no continuity on the right side of the line, a continually dinged up OBJ who was a shadow of his former self (and salty about being in Cleveland to boot), Jarvis Landry who ran the exact same 40 time as Cade Otton (4.77) and no real other receivers to speak of (after Landry and OBJ the next most catches not going to RBs were the vaunted Demetrius Harris and Damion Ratley. His coach had hired Todd Monken as OC who put in a system, but then Kitchens decided to be the playcaller. And again, he emphasized the running game and passes to the RBs in the flats (more of an Erhardt-Perkins style like the Patriots would run). So the play design would call for the WRs to run deep routes, but the play calls tended to emphasize short routes.
It's no surprise that Kitchens was fired, what's surprising is they didn't do it until after the season ended. Now don't get me wrong, Mayfield did play poorly and had a lot of bad decisions in 2019. It's one of his tendencies when he doesn't trust his o-line. Happens to a lot of QBs, witness what we saw with Brady in 2022. Brady's just far better than just about anyone ever at bailing out on a play he knows is doomed to fail (taking a sack or throwing the ball away). But Mayfield's coaches and the play calling lead to a lot of the issues on offense in 2019. Combine that with the turmoil they had on defense that season with Myles Garrett's suspension from swinging a helmet at the Steeler's QB and it was a recipe for a lost season. Cleveland's defense wasn't into it after Garrett was suspended. In the final six games, they had four games where they gave up over 350 yards. In the first ten, they'd done that three times. In that final six games they ended up 2-4 to finish 6-10. Before Garrett gets suspended, even with a 4-6 record they were in the hunt for a WC spot being two games behind the Texans.
In 2020, they bring in Stefanski, who installs a west coast system. Far better suited to Mayfield's skill set as it emphasizes quick, high percentage passes. Not only that, the new FO brings in some good free agents - perhaps most notably Jack Conklin at RT (who proceeds to be named a 1st team all-pro after that season). They get a pass-catching TE in Austin Cooper, drafted a decent LT in the first round (not great, but better than the three guys who started there in 2019 that were no longer in the NFL within a year) and got stable play out of their RG as well (probably because of Conklin's presence). Over the course of the season, the only spot on the line that has someone who doesn't play in every game is the RG. With the West Coast offense installed, the play calling also shifted to being more balanced. It's about as 50-50 as you can get, 501 pass plays, 495 run plays.
As we all know, we've had three OCs in three years since Mayfield's been here. Big difference is all three of them use a version of the West Coast - so same basic concepts. This season, Grizzard is using essentially the same offense as last season with a few tweaks. So, Mayfield's been in the system best suited to his abilities both of his seasons so far, he's had more support around him without the pressure of being the 'savior' he had on him in Cleveland.
Now I know I said we'd focus on 2019 and 2020... but we'll get some extra work done here with the 2021 Browns season as you'll likely want to point to that in your rebuttal. 2021 sees the Browns return to issues with the o-line. Conklin gets hurt in the 5th game, only plays partially in two games before going on IR. Mayfield tears the labrum in his left shoulder in game 2, makes it worse in week 6 and the team only makes him inactive for the next game. Knee sprain in week 10, misses a game because of a Covid outbreak (also missing the game was Stefanski, Landry and Clowney). Willis, the starting LT injures his ankle in the first game. Plays through it but ends up out for the 5th and 6th games. Injures his knee later in the season, ends up missing two more games (This is the same player who make a 'business decision' to not play against the Ravens last season after a knee injury the week before). Chubb misses two games with a calf injury and plays the season with a knee injury. The only skill position player available for all 17 games is D'Earnest Johnson. WR with the most games started is Landry with 12. On defense, Garrett is the only player to make it 17 games. Only one other starter appears in 16 games.
So, we have a team with diminished line play due to injuries, a QB dealing with a torn labrum after the 2nd game (while on the non-throwing shoulder, it affects the throwing motion and usually means diminished velocity and accuracy), a number of games lost by offensive skill position players to injuries and the same situation on defense. With all of that, going into that week 14 game against the Raiders with so many players out due to Covid and other injuries, they have a winning record and a win will put them in first place for their division. Of course they lose on a last second FG to the Raiders and instead of being in first, they're now in 4th because of how tight the division is. The Browns finish 8-9, with Case Keenum being the starter for two of the wins (at Denver with Mayfield out because of his shoulder, Denver goes 7-10 and fires Fangio at the end of the season and the season finale against a Bengals team that rested everyone - Chase played a total of 5 snaps, no other skill position offensive starter played and zero defensive starters got a snap - they trotted out Vernon Hargreaves III as a starting CB that game).
So, Mayfield's 2021 wasn't as bad as some make it out to be as the Browns were their typical snake-bit selves. He had them in contention for a playoff spot (and a division title!) deep into the season before the rails came off the season due to injuries.
