There's definitely others that shared your perspective. A commonly cited reason of early Figma adopters was that they felt it was faster than Sketch.
Of course, the reality was that performance is a super nuanced thing. It's always measured in relation to specific things, but ultimately summarized via a "feeling".
Aspects of performance include:
- Loading a (blank/medium/large) file from (scratch/cache/etc)
- Performance when editing (what?), panning, zooming (small or large doc?)
- Performance with a large number of simple objects, or complex objects (components? variables? nested components? drop shadows/background blurs?)
I haven't personally done some performance comparisons between the two apps since ~2018 but at the time there were definitely things where Figma was noticeably faster than sketch, a lot of things that were comparable, some things that were slower. My own very biased feeling was that Figma was faster more often than not but it's always up to the individual use case, how their file is setup, what they are doing within that file, and how they mentally weigh those different scenarios.
I definitely didn't feel like being on the web was a limiting factor. In some theoretical state, with infinite resources to optimize everything, native could be faster since you have access to lower-level APIs. In practice, that's the same argument as "it could be faster in hand-written assembly". Almost never did we get to the point where we'd use those abilities even if we had them, due to their cost on development and impact on the correctness/maintainability of the code.