About the villains in super hero movies: the problem comes from the differences between the two media. In comic form, each super hero has hundreds of stories, which forces to reuse villains, which means they must be very powerful to survive the clash with the hero and come back later with a new plan that will, once again, be thwarted. In movie form, you will never be able to tell more than a handful of stories before you need to reboot the franchise (because films take long to make, so both your actors and your audience age, meaning you need new starting points for new spectators every now and then). With dozens of villains to cram into five stories, it's tough to make any of them recurring. Most will have to be introduced and dealt with within a single story, as a result, you can't go too crazy with their power level. Note that Loki was mentioned as an example of a well done villain, but he is one of the rare recurring villain.
