In Spector.js it looks like the demo is using a very small number of draw calls, and those can sometimes have hundreds of thousands of triangles. For old low-end mobile GPUs this might start to become a problem, but it's nothing for the last 20 years of desktop GPUs.

In any case, it looks like a good base for further optimisation to ignore offscreen UI elements early (e.g. not sure if egui has something like Dear ImGui's ListClipper).