Don't know why you're being downvoted. These all are perfectly reasonable concerns. I've seen many GUI frameworks fail because of a mix of these reasons.
I was writing POS applications in the 90s. And ringing up customers needs speed and responsiveness. Windows was way too slow at the time, that's why POS applications even to this day often still work in character mode, or DOS-graphics.
PS I know it's becoming less and less of an issue these days, but you get my point.