This is true but also false.

It’s true that things could be slow on those old machines, especially when it had to hit disk. It’s true that things were often single threaded and would stall.

But what’s also true is that this old code was orders of magnitude more efficient. Put that code on even a modest machine from today with an SSD, even a Raspberry Pi, and it would scream. Everything would be instantaneous.

Some of the reasons for this degradation are unavoidable, like high DPI displays and feature depth, but a lot of it is just bloat on top of bloat on top of bloat.