There was not really time to develop all the characters in the time frame, while telling the story.
I agree completely. And as I said I love the movies. I've watched every single one from the very beginning right through until now.
But like you said, with so much going on in every film, they often don't have time to flesh out the character development fully, or show some of the emotional impacts of certain events.
But Wandavision has done a great job at exactly that, fleshing out the toll taken on Wanda ever since she lost her parents to the emotional impact of being a super hero and losing the people you love in doing so.
And if Marvel can start using the Disney+ series to develop these characters even further while also moving towards significant plot points like they have done with Wanda so far, I think it adds another really great dimension to the MCU that should make the feature length movies even better.