The sad thing is that even running DOS software in DOSBox (or in QEMU+FreeDOS), or Amiga software in UAE, is much faster than any native software I have run in many years on any modern systems. They also use more reasonable amounts of storage/RAM.

Animations is part of it of course. A lot of old software just updates the screen immediately, like in a single frame, instead of adding frustrating artificial delays to every interaction. Disabling animations in Android (an accessibility setting) makes it feel a lot faster for instance, but it does not magically fix all apps unfortunately.