So it's modular. This is normally considered a good thing. It means you don't have to pay for features you don't need.
The ISA is open so there's no greedy corporation trying to upsell you. I mean there's an implementation and die area cost for each extension but it's not being set at an artificial level by a monopolist.
It's a good thing in many cases but not if you're going to be running applications distributed as binaries. Maybe if we go the Gentoo route of everybody always recompiling everything for their own system?
Then you stick to RVA23, which is comparable to ARMv9 and x86-64v4.
But that means a port of Linux can’t be to RISC-V, it has to be to a specific implementation of RISC-V, or if sufficient (which seems still debatable) to a specific common RISC-V profile.
You can target the minimum instruction set and it'll run everywhere. Albeit very slowly. Perhaps you use a fat binary to get reasonable performance in most cases.
This isn't easy but it can be done (and it is being done on x86, despite constantly evolving variations of AVX).