Not sure what you're on about.
By the time the spec was first ratified (2019), RV64GC was already the densest 64bit ISA, and it's not even close.
Because all other 64-bits were designed with no regard to density too. On 32-bit (and thats where density matters) it's sill worse then Thumb even with compression extension.
Thumb is really good, but this is no longer true as of late 2021, when bitmanip and the code reduction extensions landed.
RISC-V is currently the most dense 64bit ISA, as well as the most dense 32bit ISA.
Because all other 64-bits were designed with no regard to density too. On 32-bit (and thats where density matters) it's sill worse then Thumb even with compression extension.