Even if that were the case, recompiling Debian with different compiler options is not rocket science—thanks to decades of tireless work by thousands of volunteers.
Probably someone will read your comment and think "the C extension" means "support for the programming language C", but that is not the case. Standard RISC-V instruction set extensions are identified by letters: M for multiply (and unfortunately divide), F for floating point, D for double-precision floating point, A for atomic memory operations (necessary for SMP), V for vector operations, and so on.
The C extension is the "compressed" extension, which represents the most common instructions in 16 bits instead of the usual 32. Without the C extension, RISC-V code is relatively bulky, which is a disadvantage not only for limited-memory microcontrollers but also because, if you have an instruction cache, less code fits into it, so most software runs slower. With the C extension, RISC-V code density is at least competitive with the best alternatives like Thumb2, and in most cases slightly better. This is particularly interesting in the 64-bit space, because arm64 (aarch64) has abandoned the Thumb2-style compressed instruction approach.