Honestly, for me, the proof really is in the reaction to losing Shaw and Martinez.
I actually liked what he was doing last season in setting up to an extent, but a few things have bothered me since the summer.
1. The preseason - similar to Ole, it almost felt like we didn't have one. He didn't work on truly implementing style and getting players adapted. For me, there was a real lack of urgency, even in his selections. For a team looking to win trophies, you cannot afford to be as casual as we were, that comes from Ten Haag, not the Glazers.
2. The impact of losing Luke Shaw and Malacia - I've seen teams have bad spells losing players, but not thier whole game coming apart due to simply losing a left back. This has always been an issue for me with ETH. It almost feels like every position needs to be in place for his system to work, which is a really bad sign as injuries will always happen. It's not just that we aren't as creative or sharp, it's that our entire style of play seems to have been ruined by losing a CB and lb. That's ridiculous. Somehow, we can't build up, hold possession or create chances because we lost our left back. I've seen City, Arsenal and Liverpool lose players. Barca have most their xi injured, yet their style of play is still evident. It's such a ridiculous notion and an excuse we shouldn't be accepting as a fanbase. Last year, we needed a specific profile of striker, now it's this.
3. This idea of changing style of play to suit the club. No one asked for that. The club brought him in for his style of play. My honest guess is that the pace and width of the league might not pair well with his tactics and he's noticed it.
4. Transfers - Again, the idea that we NEEDED on specific player from Barca to be able to play the way he wants to play is rubbish. Other teams have less talented midfields who can move the ball forward and hold possession. In addition, he had the option to buy that. He hasn't been held back. He chose Mount. Casemiro, even currently, should be enough for any manager. He bought Antony. He bought Malacia. At no other club would people look at the DOF, when the team has spent money, and blame him. If Newcastle's transfers didn't work, people would blame Howe. When Rodger's didn't work, they blamed Rodgers. Only at United are the club hierarchy blamed for getting the players in that the manager wanted, because every manager is the Messiah.
My conclusion is that, it's ok to sack managers when it isn't working. Expectations are set and quick decisions need to be made when they are not met. This isn't United in 1989, this is a global powerhouse. Madrid wouldn't