It completely depends on the reason why he was successful elsewhere. He might have been successful because his system was unique and countered the typical styles of the times. If people are familiar with things like online gaming then they would have heard the term "meta" being used regularly. That is basically where a certain setup has advantages over others and whoever discovers it first gets a big boost in ranking beating people they shouldn't until everyone else is also using that setup and then the counter to that setup becomes the best option aka the "new meta". This applies to all games that are competitive and football is no different.
We know Wilder has a unique system but the whole press from the front thing is much less effective now that teams have filled their defences with ball playing centre backs and can play through presses. The overloads from the centre backs are no longer a surprise and can be countered with an effective counter attack.
Was he successful because of his ability to man manage people, manage a game effectively by making the right changes at the right time, alter his system to suit the changes within football etc or did he find a system that worked and stuck with it? If it is the latter then there comes a time when the system stops working because everyone knows it and they know the counters to it. I'd guess that his 1st season in the PL with Sheff Utd showed it working and it got a lot of attention and analysis but then his 2nd season showed what happens when teams know what you are going to do.
My guess would be that he has probably been a bit of both across his career but his abilities as a manager are only good and not great where his system was great but is now too easy to counter and he's out of ideas. His good abilities were enough in the lower leagues but more than good is needed at the higher levels.
