But all forms of coding and media editing (the main tasks that are truly CPU/GPU-bound, the area where something like Mighty would help) have remained as local desktop app affairs.
I think what really happened is folks misinterpreted the significance of Figma. The web has taken over in collaboration-focused software, e.g., things like Google Docs, Slack, etc... What really happened is that design has moved from specialized professional software (hard to use, powerful), to being more like collaboration software (easy to use, light).
I.e., what Figma really signals is that design is now more like new task that became more like using Google Docs app, not that high-powered tasks like video, photo, and audio editing are becoming web apps. This means what really powered Figma's takeover was that flat design took over, which is less technically demanding.