For most of what you say, I agree, but Ant-Man and the X-Men both have a reason to be exceptionally fit.
Lang is (was) a catburgler, and at some point had to be in condition for scaling buildings and whatnot. It's believable that he formed a habit of intense fitness regimes.
As for the X-Men, intense training has always been a part of their history; they made more out of training as part of their schtick than anybody else in comics. Several points along the way (notably New Mutants vol. 1, no. 1), the point gets raised that mutant powers are a function of mutant physiology. So in order to develop both their abilities, and their control over their abilities, requires that they hone their bodies.
That panel of emasculated Hawkeye is not drawn by David Aja. It’s Leonard Romero.
Good Marvel characters- Bring Them Back!!!
For the purposes of discussion comparison and contrast, here's some art from John Buscema who no one would accuse of trying to erase the differences between men and women.
Here's his Hawkeye. While athletic, Clint is kind of lean.
Jonah Hex and Superman aren't relatable, yet they can still be plenty interestin'.
DC, please give Jonah Hex a new solo.
Here's his Carol. While obviously meant to be pretty, a far cry from the balloon/stripper proportions she gained in the 90's
Another interesting picture for comparison. Clint is the the least muscular looking of all the men. All the others are ripped but the only one who's really bulky is Hank Pym.