The way the Marvel movies have largely worked up until now have basically been the most expensive TV miniseries in history.
Yes, and that's exactly what's so interesting about them. It's a form we haven't really seen in movies before. It's an innovation. How is that bad?
Heck, television has been a far superior storytelling medium to movies for a long time now, in large part because it has more time to develop its worlds and characters in depth, and because it's in the control of writer-producers with clear, consistent creative visions rather than directors who may be concerned with style over story. There are so many movie series that lack any consistency, so many individual movies that are just not very good. The only advantages movies these days have over television are budget and time. So if the creative process in movies begins to follow the lead of television, I don't see the problem.
And just as importantly, it's following the lead of the comics. Look at how
Ant-Man was enriched by its ties to what previous movies had established. We already knew the SHIELD and Hydra backstory, the larger rules of the universe, so here we saw a story set against that backdrop, able to build on it to give the story's world substance and resonance without the need to start from scratch. When Ant-Man needed to prove himself in action, they could bring in an established hero, the Falcon, as a guest star to fight him -- exactly how the comics would do it. Superhero movies in the past have rarely captured the feel of the comics that well because movies are so much more standalone than the serial structure of comics. The MCU movies are more of a serial, and that's good, because it brings them closer to the structure and style of the comics they're based on.