I don't use either, but isn't Figma a web app, while Sketch is a native macOS app? Then I would choose the native app any day. Correct me if I am mistaken.
Maybe if like 93% of the population, you, or the people you share your work with, are not running macOS.
I've never seen anyone doing graphics design etc and not using a Mac to do it.
Hello, I’m one of them! For context, I’m a software engineer but also do design because I have to (startup, a free no/code website builder, boomla.com). I even bought a Mac for running Sketch but I just couldn’t use both platforms because of their differences (keyboard shortcuts).
I guess there are tons of part-time-designers who don’t switch.
FWIW maybe Sketch fixed their stuff, but in 2018–2019 Figma's performance was just so much better that I switched and never looked back.