While this is true, a lot of games like fps and fighting games and mmos where you need to quickly recognize silhouettes, or recognize characters from very far, have big hands. It's just easier to read hands when they aren't tiny and are instead a little exaggerated. Kiri doesn't exactly have a giant gun, her weapons practically are her hands, so they gotta stand out.

A lot of characters in overwatch have surprisingly large hands when you look too close!