It was GUI defined manually by pixel coordinates, having more flexible guis that could autoscale and other snazy things made things really "slow" back then..

Sure we could go back... Maybe we should. But there are lots of stuff we take for granted to day that were not available back then.

RISC OS has the concept of "OS units" which don't map directly onto pixels 1:1, and it was possible to fiddle with the ratio on the RiscPC from 1994 onwards, giving reasonably-scaled windows and icons in high-resolution modes such as 1080p.

It's hinted at in this tutorial, but you'd have to go through the Programmer's Reference Manual for the full details: https://www.stevefryatt.org.uk/risc-os/wimp-prog/window-theo...

RISC OS 3.5 (1994) was still 2MB in size, supplied on ROM.

The OS did ship with bezier vector font support. AFAIK it was the first GUI to do so.

P.S. I should probably mention that there wasn't room in the ROM for the vector fonts; these needed to be loaded from some other medium.