I'd rather ditch humans, dwarves, and elves, than halflings and gnomes, when building a world.
For a long time, I didn't like dnd halflings, and had only ever played one halfling character, and they were a halfling primarily because I wanted a semi-coastal farmer's kid turned thief from Sembia, and that backstory just fit a halfling better than a human. Eventually I formed a more fully realized understanding of halflings, and consider them important to DnD.
Halflings and gnomes have one thing of importance in common, and it ain't size. It's curiosity.
Halflings are possessed of incredible curiosity, and while many love the simple life, they are capable of incredible action when roused. They're also noticeably more nimble than humans, but smaller, and most people take them less seriously because of their size and youthful visage. You either can see the appeal of that or you can't.
Gnomes are similar in curiosity and liking to have their communities left alone while being friendly and social individually. They're also very bright, creative, and their curiosity is less about the world in front of them directly, like an explorer is curious, but more the curiosity of the scientist, the delver into secrets, the inventor. "Can I make this?" rather than "What's over that hill?" For Rock Gnomes, that is about invention, physical science, etc. For Forest Gnomes, it's more about magic, and nature.
Oh, the other thing that both races have that a lot of players want is comfy homes just under the surface. From David the Gnome to Hobbits of the Shire, it's dope as hell to imagine digging your home into the hillside or amongst the roots of a great tree.
Gnome Home - Tiny House Blog
Now, the 5e gnome is sub-optimal thematically in that the Rock Gnome gets next to nothing of actual value from it's subrace, and the Forest gnome is the only one that gets to talk to small animals, but that's easily fixed by making it explicit that Rock gnomes can make things like repeating crossbows, and upgrades for the range and power of bows of all kinds, with their tinker tools, as well as improved block and tackle designs, etc, and giving the base race the ability to speak to small and smaller beasts. Minor illusion is really useful, so IMO that makes the two equal in power and makes it so that all gnomes can talk to small or smaller beasts.