Can you use Adobe Animate to make full feature movies? Or is it only used to make animation for web?
You can export HD or even 4K videos from Animate. It might take a lot of drive space though.
I think Animate is used a lot in TV animation production. For a future film you might well do a lot of the work in After Effects or Premiere, Animate isn't good at doing advanced video effects.
You can indeed do that using Flash/Animate. Sita Sings the Blues was animated in Flash/Animate and many other films have been done that way. It's true you can't composite much with it (yet) but After Effects fills that gap nicely.
Here's a list of films animated using Flash (Animate)