With intelligent frame pacing you can sacrifice, say, a frame of input latency to sustain high frame rates. See https://raphlinus.github.io/ui/graphics/gpu/2021/10/22/swapc....

> Are immediate-mode GUIs up to the task? What is driving their authors to pursue this design? Why aren't they choosing a declarative design

Immediate mode UIs make managing state much easier, and avoids callbacks for event processing. That alone is worth it in my opinion.