While it is a known fact that the late Stan Lee created some of the great superheroes of comicdom, one of the things that set Stan's writing apart from other writers of his generation was the humanity of his characters. Spider-Man, one of his most well known creations was probably just as famous for being his alter ego, Peter Parker and all the difficulty that entailed. Stan did the same on his run on The Avengers which seemed to begin as one of those books that was designed to showcase heroes who floated other books (Iron Man and Thor, among others) much in the way the Golden Age All-Star Comics used the Justice Society of America. But with the re-introduction of Captain America in issue #4 (And all of the angst Steve Rogers would feel being a hero out of his own time) and especially after issue #16, where the Avengers became Captain America and a motley crew of former villains, Lee still never forgot the humanity of his characters.
Avengers, vol. 4 falls between the end of Lee's run on the book and the introduction of Roy Thomas as the writer of The Avengers (under Stan's tutelage of course!) The end of Stan's run has the Avengers facing off against the racist Sons of the Serpent, which almost takes on an allegory type vibe. As a Jew who reached his majority during World War II, I'm sure Stan was probably the target of antisemitism, so this makes some sense. Less successful is the original Incel, the Living Laser, who hatches a plot to kidnap the Wasp because he sees her at a party and thinks he's the most beautiful woman he's ever seen--surely destroying her teammates and helping a rebel group overthrow a third world dictator will prove his love, no? I realize that it was the 1960s, but these "damsel in distress" yarns don't age well and it just comes off as some sort of sexual assault.
As for Roy Thomas--this isn't "Kree/Skrull War" or even Vision/Ultron Thomas, which is Thomas at his absolute best. Even though he takes over the scripting chores for the second half of the book, you can still see Lee's heavy hand--he is given top billing in the credits as "the Editor." We're probably still a bit away from when the book become's Thomas' and all that entails. Yes, Lee was an innovator, but Thomas and contemporaries like Dennis O' Neil were able to take these stories to the next level--one would never think of Stan Lee giving Tony Stark a drinking problem that would sideline him as Iron Man. It was this next generation of writers that did that, but Stan laid the framework.
In the introduction, Thomas reiterates several times that he wanted to add Thor and Iron Man back into the Avengers, but Lee wouldn't have it. So he made due with what he had and it's a good, but not great start. I think he knows that and is disappointed by that, but still...writing The Avengers was a huge opportunity and he capitalized. Just not here. Not yet.