What you've basically said here is "he persisted with a shit formation for too long. He is capable of changing it and bettering our side tactically and in results as evidenced by the end of the season, but I want to sack him now because it took him too long to do that".
Sounds like firing out of rage rather than evaluating pedigree to be honest. Whilst agreeing he should have tweaked when he had injured players, I don't think he has gaping flaws that many other managers don't have. Remember, his medical team is broadly shit too, if they have miscommunicsted and misjudged injuries (which they've proven to do), it hampers planning.
He was too stubborn for too long but insinuating he's not adaptable and outright won't learn form his mistakes is presumotious.