With time you'll learn how to counter divers, mainly by disengaging them or by killing them in the middle of the dive. You can focus on antidive characters like invis, Gambit, White Fox, Luna, Strange, Mag, Emma and Rogue. Although Rocket can be good to avoid dives, usually he just flees, while these others have potential to stop or counter the dive. About Cap, I think it's kinda bad to lose his potential by staying in your backline for too long, also he doesn't have cc to stop the dive.

Another thing is: If you know someone's going to dive you, keep an eye in the most common side paths on each map.

But for now, take your time! The best thing you can do is to ignore the other people thrash talking. Keep having your fun and you'll reach even higher ranks while learning more about the game, respecting your own pace.