Zero allocation impl? very cool! Arguably, the original runtime should have done this in the first place given the limitations/tradeoffs aren't so bad, but I guess that ship sailed 20 years ago (man that hurts)
Unity inherited a much simpler Boehm GC from Mono. Under a (single generation) Boehm GC allocations are a bit more expensive and garbage collection sometimes a lot more expensive. (A Boehm GC was much easier for C++ engine code to understand/interact with, which is also part of why the .NET modernization project for Unity got so complicated and still has such a ways to go left.)
[0] Fun aside: in fact, modern docker advice for .NET is to switch "server applications" to use "Workstation GC" if you need to stack multiple containers on the same host because of differences in expected memory usage.