I also hope for longer films, but therr are ways to cut the right stuff. I think you are right, though. Chiaki Kon likes to copy paste the 90s show way too much to use something more dynamic and less stock-footage. I just feel like now that is is a film and not series, they need a less repetitive approach. I think 100 - 110 minutes would be perfect.
I don't think season 3 has stock footage becaus Chiaki Kon likes it, but because season 3 was supposed to be closer to the 90s anime, since fans all over the world were missing the feel of the original anime had. And of course, also to save time/money.
Yes really, because A.) you know TOEI is going to pad the movie with stock footage. It's what they do and B.) Dream arc might not be as long as others but it's still got a ton of material to cover. If the movies are 90 minutes apiece that's the same as giving each chapter about 15 minutes of screen time. That's not a lot.
A) stock footage doesn't make much sense in a movie because we'll probably see the senshi only once transforming and attacking in each film. Of course it all depends on the script and if Toei wants to cut the movies later into episodes, which I think would be a bad idea.
B) yes there is a ton of material and there will be cut a lot because it's necessary. Usually when there is a film adaption of a novel, they have to cut a lot of stuff to make the plot work for a film, since narrative structures in film follow mostly patterns.
I rather have an anime that tells the story of the Dream arc in an original and new way, faithful to the source material instead of a 1:1 adaption, using the manga as a storyboard (like Crystal did so far), because that won't work anyway.