The Peter Principle applies to Moyes. Promoted above his talents.
On reflection, Moyes was always a very good Championship level manager. Disciplined, defensively good, emphasis on hard work, but limited in their tactical awareness. In essence he took over at Everton when we were, in all but name, a Championship level club. We'd been flirting with that level for years, so it was a good fit for Moyes and us. He came in and made us a very good Championship quality team that competed well above any right it had to expect (with the blip second season left out of the equation). I've always believed the PL (especially back then) to never be of the quality its always afforded. Any club offering a lot of effort and discipline can achieve a fair bit. He got that out of our players and he got a lot of leeway from owners who were not ambitious (on or off the field). It was perfect for him. As soon as he left Everton though he had to show his own coaching credentials (and man management credentials at clubs with players unwilling to just accept his view of things and a discipline oriented regime).
He's what we all suspected him of being when he was here: a bog standard manager with a good eye for a bargain and an ability to impose discipline...but only at a certain type/level of football club.
Yes I think all of that has proven to be the case. The premier league when he was operating was in terms of excitement a very poor league. You probably had 14 or 15 clubs who were little more than championship clubs just looking to stay in the league. At the other end you then had 4 teams who were amongst the top 10 teams in the world. It was a complete monopoly and any one of the top 4 back then would probably walk the league now.
Obviously the strength of the top 4 teams gave the league an excitement and buzz to Sky in particular, who's base is largely made up of their fans as they competed to win every trophy going for a 5 or 6 year period. Outside of them though it was a dull league not too dissimilar to Scotland.
That was the context Moyes thrived in. He knew the logical limits of what he could do, which was make as few mistakes as possible, don't get distracted by cup competitions and look to be as close to the best of the rest as possible. Nobody minded as the people who run the league (execs at Sky) had no requirement for more competition to the top 4. It provided more than enough entertainment. 4 sides going for the title with 8 sides in a mass relegation scrap. This always afforded Moyes a level of respect in the game he may not have been due.
Where I think football has moved on in the Premier league is more egalitarian now. However just standing still and being consistent will only get you so far. If you look at how your Palace's, Southamptons or Leicester's are attacking this season there is a different approach.
I think Moyes is of a very particular time. His biggest mistake was not moving on once he established Everton are a top 6 team for another challenge. It may have stopped him getting stuck in a certain way of thinking.