As for program size, I played with small algorithms (like binary search) on godbolt, and my x86 programs had similar size to RISC-V with compressed instructions. I rarely saw 1-byte instructions, there almost always was at least one prefix.

> e.g. a single 32-byte x86 cache line could have up to 32 instructions where the original RISC-V ISA might only have 8

With compressed instructions the theoretical maximum is 16.

> so they have to deal with the problem too.

Luckily you can determine the length from first bits of an instruction, and you can have either 2 bytes left from previous line, or 0.