Unfortunately, that which the headlines giveth, the implementation details taketh away.

The bulk of the savings come from loads and stores to the stack. The remainder of the savings is for destructive integer ops on a subset of only 8 registers.

So sure, if your code can be efficiently described using those restrictions, then you'll have great code density! Many commercial codes do have short stretches that fit this requirement, but they are interspersed with stretches that don't.

This makes it very hard to produce an effective code size benchmark for RISC-V, because it is so heavily load dependent.