I mean, I might be missing something, but Whirlwind would be horrible as a main villain. He doesn't bring anything to the table of note, other than being an Ant-Man villain in the comics. No thematic resonance, no good comics storylines to adapt, he needs a new origin that's completely separate from Pyms and thus less impactful. His powerset does not help show off the Pyms' power set, he's not an intellectual rival. Every adaptation of him I've seen he's kind of a thug.
Originally Posted by marcvader
Ultron is waaaayyyy too much for the Pyms to handle on their own.
Hmmm... yes and no. Most of the AI we've seen defeated in films have been defeated by vastly underpowered people. Someone who shrinks is exactly the kind of person who could defeat Ultron on his first outing. Perhaps he can come back with a bigger power base like Loki did for an Avengers film, but the idea that 'Movie Ultron = current fully evolved Ultron who's battled the Avengers ten times' would, by necessity, be incorrect.