There are lot of Genius Archetypes that gnomes could benefit from.
The Great Detective. Think Sherlock Holmes, a brilliant character with an eye for detail that gave him an almost supernatural edge over his peers. If you take Sherlock Holmes and you add gadgets, who do you get?
Batman, you get Batman. Batman is TOTALLY a gnome. He smart, persistent, and he uses all kinds of cutting edge tech to one-up his enemies. Most importantly, Batman STUDIES his foes. By the time you get in a battle with Batman, you’ve already lost. He studies his enemies so that rather than trying having to overpower them, he puts them in situations where their power will defeat itself.
And what about going in to an unknown situation? Gnomes should be prepared. They should plan for every contingency imaginable. Another missing Gnome Genius is The Schemer.
Redundancy, escape plans, and fail safes. We aren’t goblins. We shouldn’t blow our selves up all the time. We should know exactly what we’re going to do when something goes wrong.
The Miserable Genius/Misanthrope. Gnomes are happy and cheerful a lot, but it’s weird, because they have a tragic shared history AND they are smarter than everyone else. Any person that is significantly intelligent will tell you, when you are surrounded by dumb people you are MISERABLE. Look at House from that doctor show about House. He is so much smarter than everyone else, he can barely stand it. It’s like being stuck moving at everyone else’s slow kindergarten pace all the time.
Add Gadgets to House and who do you get? Tony Stark, Ironman. Tony is miserable, but he has a mental flame of brilliance that won’t let him rest. He’s driven by his negative view of the state of the world to try as hard as he can to change it.
These are aspects I would LOVE to see incorporated in to a gnome hero. It’s really easy to make a Misanthropic Mad Scientist Villain and call it a day. When that character decides in spite of humanity’s flaws they want to save it, magic things happen!
Thanks to @VioletExplorer for poking me with questions and giving me things to think about!