His current manager inherited a shambles, Moyes inherited the best team in the EPL.
The current manager is also a proven winner, so will undoubtedly be allowed additional leeway.
Moyes made many, many mistakes. Chasing Fabregas for 2 months being possibly the most hilarious of them all. He was never, ever going to go to Man Utd, yet they spent 2 months trying to sign him. When, as you say, they could've put their efforts in to renewing an aging defence.
Moyes is an average manager, Everton and Real Sociedad are about his level. He'll never win anything of note. He's a shitebag manager who sets teams up to not lose. That he ever got the Man Utd job is utterly baffling.