I'm not sure what gnomes really do as a PC race. They seem like "dwarf lite" to me... they're not as robust, not as good at underground stuff, and not cool enough to live under mountains (instead, they live under hills, just like halflings). So we've got something less beefy and minerly than a dwarf, less fat and rustic than a hobbit, less threatening than goblins or kobolds, but not particularly "more" of anything.
All of which is fine for a "monster manual" race. Like, OK, this is where the gnomes live and they need help because ghouls are eating them or whatnot. But great gnomish heroes? Never heard of them. We do have a bunch of mighty elves and dwarves, and even a few halflings who aren't a total embarrassment on the adventure. Gnomes just seem like quaint little dudes who are distinguished from goblins or kobolds by the fact that they probably don't start all conversations by biting you on the leg.