Well, i'm 6 foot tall, in my thirties, have been lifting weights since 15 years old but my face is 3,5/10, maybe 4/10 in a very good day. Yes i have done a lot of progress in the gym throughout the years, now i have a muscular body.
But it never made any difference in attracting females, they've ignored me before, they are ignoring and rejecting me now, only guys show some interest (are intrigued), what they can do to progress like that in the gym, and that's it!
I have two chad lite friends with 7/10 faces, and I've been helping them to gain some muscle, as soon as they started to show some gainz, women were insanely more attracted to them, like if they have ascended to true chads status, something that have never happened to me and most sub 7 guys that I know of, made no difference at all!
So, the way I see it from first and second hand experiences, gym would only make attractive males even more attractive. If you are ugly and/or small, gym won't help much. Just don't be fat because that is death sentence for males even if you have a somehow decent face.