And I am not kidding in the least when I say that. Regarding more modern operating systems, BeOS was so nice to use. Here was an OS that had UI/single-user needs baked in to it from the beginning, and it was a breath of fresh air. I'd liken it to the experience I had switching from a 60Hz monitor to a 164Hz one- I didn't really think about it much at the time, other than I wanted a gsync-capable display, and one was one sale. But the smoothness of the scrolling, mouse use, etc was so much more pleasant. And yet I never would have complained about the 60Hz screen until shown the alternative.
Venturing in to personal opinion, I'd also say BeOS was developed at the inflection point between engineering running the show, UI be damned, and where we are now, with designers running the show, actual capability be damned. It was a good mix.
As a C=128D owner, I hear you loud and clear. It's a slap to the contemporary programmers' faces that a 1 MHz MOS 6510 based system was more responsive than multicore GHz, hardware accelerated systems we have now.
I find it very noticeable, not least as in terms of those basics we seem to be stepping backwards for responsiveness.
Loading software should be quicker, but no one cares about space and size any more, especially as more and more becomes a front for a browser. Even native software is faintly disappointing. You load a game in seconds from the lightning fast SSD then it takes 2 min to load the save as that's bigger than some OS's. :)