And that design is generally regarded to have been a mistake, results in very bad code density.

ARM went out of their way to remove it. Multiple times, with both AArch64 and the various implementations of Thumb.

I can't imagine the pressure at Acorn, with the Olivetti acquisition impending, on Furber and Wilson to deliver their design unoptimized for the required task.

A CPU for this century is not the one for last?

Risc-V has always seemed like a 20th century processor to me, heh.

Given its origin from MIPS, it kind of is.