Arm was one of the CISCiest of the RISC processors at a happy medium in instruction complexity that gave them all the simplicity of regular sized instructions while still getting the job done in fewer instructions than a more ideological RISC ISA.
Also, getting the job done with fewer instructions meant requiring less RAM in embedded roles where it thrived before entering the market from below in classic disruptive innovation style, the same way that x86 entered the server market. The other RISCs were mostly high end workstation or server chips suffering from low volumes. I actually ported some software from an SGI MIPS box to x86/Linux once. It was a nice system and I see why people liked it but it just couldn't keep up.
>that gave them all the simplicity of regular sized instructions while still getting the job done in fewer instructions than a more ideological RISC ISA.
Thumb2 in 32bit ARM was competitive in code density.
AArch64 code density is abysmal, dramatically worse than RV64GC.
Some in depth look at various features here:
https://userpages.umbc.edu/~vijay/mashey.on.risc.html
Also, getting the job done with fewer instructions meant requiring less RAM in embedded roles where it thrived before entering the market from below in classic disruptive innovation style, the same way that x86 entered the server market. The other RISCs were mostly high end workstation or server chips suffering from low volumes. I actually ported some software from an SGI MIPS box to x86/Linux once. It was a nice system and I see why people liked it but it just couldn't keep up.