Ant-Man/Giant-Man/Goliath/Wasp/Yellowjacket size changing is done in a fast as you can blink continuous motion in the comics which is something that doesn't look good on 2d paper but would look good in live action which is what Edgar Wright has said. Often in the comics Ant-Mans fighting style was to shrink to avoid a enemy throwing a punch and then regrow and punch them back all in a flash. Something like that would look great on screen. He utilized the element of surprise. The stealth aspect often worked for him. I always thought Shrinking or growing isn't any more goofy than Mister Fantastic stretching when you think about it. Will Pym or Lang use different ants like flying ants, fire ants, ect or create giant ants? As Giant-Man/Goliath the growth process required the rapid acquisition of bodily mass, presumably from an extradimensional source. This extradimensional mass fortified all of his cellular tissue, including his bones and muscles, enabling him to support his increased weight, and giving him superhuman strength.