This is an app I started in 2008, and at the time getting the speed of native was important to me. I work with very large "sheets"

I also wanted to get to something which could be useable for me as quickly as possible, which at the time for me meant a native app. I also wanted local file storage etc.

Agreed that in 2021 you could probably make this work as a webapp, though I think it would still be a challenging engineering exercise to make it fast.