Yep, when it worked it was a thing of beauty, which is why he was so loved (and is equally still well loved at all his former clubs).
I agree, if we hadn't changed managers last season we'd have gone down as things had clearly stopped working (though other fans would disagree).
And yes the problem was that players were exhausted after 4 years of his methods, players were injured left, right and centre and his desire of having a small squad meant not enough back ups. It's also arguable that we'd been found out to some extent, teams worked out how to play us.
Having said all that, the first 3 years under him were special, he got us promoted after 16 years in the wilderness and gave us the 3 best years in our recent history.
To rebuild a club, change the mindset and way of doing things, there is none better, even if his teams ultimately have a shelf-life.