tl;dr: this is actually Iron Man 5: Son of Iron Man (Iron Man 4 being CA:CW) to the detriment of Peter Parker’s own development in this incarnation.
I get that RDJ is incredibly charismatic and, probably more importantly, incredibly bankable. He has made Tony Stark a role impossible for another actor to step into. And so rather than recasting the role as he ages, Marvel is maybe thinking that they can turn him into the Professor X of the Avengers. (Pure speculation on my part.) But… But. There is a point of oversaturation and I fear we might be getting close to it.
Not everyone goes to the MCU movies for Tony Stark – or, rather, just for Tony Stark. People want to see Steve Rogers most in a Captain America movie, they want Peter Parker to get all of the best scenes in a Spider-Man movie. They want an ensemble in the Avengers pieces. They don’t want Captain Jack Sparrow (and Friends), Plot Coherence Not Necessary because, unlike Captain Jack, the MCU characters have histories that go back decades.
But judging by the endless stream of Pirates movies, I’m not sure Marvel/Disney particularly cares about that. They might be able to safely assume that the comics fanpeople are going to pay to see the movies regardless but in order to attract new eyeballs, they go with what works. And if what works is Tony Stark everywhere, then Iron Man 6: Infinity War is up next.