>But I also don't need to spend an entire weekend setting up a PC and a printer for my mom anymore either. I don't need to teach her arcane commands to get basic functionality out of her machine. Plug and play and usability happened
The slowness is orthogonal to all those things that have improved. We can put the fast back just fine while keeping those things.
I don't think you can, not really. Practically all the slowdown you see comes from increasing levels of abstractions, and basically all good abstractions have a performance cost.
Abstractions in general buy you faster development and more reliable/stable software. UI abstractions buy you intuitive and easy to use UX. All of these benefits define the modern era of software that has spawned countless valuable software programs, and it's naive to think you can skip the bill.
The slowness is orthogonal to all those things that have improved. We can put the fast back just fine while keeping those things.