It's pretty impressive that a browser based app can compete with such a complex and performance sensitive app like sketch. I understand why sketch is a native Mac app but having no windows or Linux port leaves the door open for competition.
Interestingly, my issue with Figma is just that—it feels slow and clunky to me, I imagine largely because it has to run in a browser. Surprised so many people prefer it.
For me it's the other way round. Figma canvas is silky smooth while Sketch drones on.