I kinda doubt it. That machine has 72GB of RAM and everything can fit in cache. Also, building a very much larger C++ project (e.g. Firefox) can saturate all the cores no problem.
That's one of the biggest problems with rust. In many cases, the dependency graph is such that not a lot of crates can be compiled at the same time. Compound with the fact that building some crates can takes minutes, and overall build times can be terrible.
Just look at the CPU usage on a >= 16 cores machine while building the rust compiler itself. The only time all cores are used, essentially, is while building LLVM.
