The constraints on data visualization are not the same as the constraints on an IDE, which is closer to what we were building. Also, our users could definitely "process" the data faster than it could be rendered, because what they were doing most of the time was skimming through it for points of interest. They were not sitting and deeply considering each data point one at a time; they could glance at a page and know in a moment whether what they were looking for was there, or whether they needed to scroll further, or whether they needed to tweak the query and re-run it or click a link to a different screen. It was muscle-memory for them, and the tiniest hitch was frustrating to the user experience.
Most "performance" problems on the web are solved by simple techniques like virtualization, pagination, pushing expensive calculations to the server, avoiding round-trip requests, or basic UI/UX improvements. The only time I would care about JavaScript's actual runtime performance if I were doing something crazy like 3d rendering in the browser and that's a completely different set of problems than React or Yew are set up to handle.