No, in this case it pretty much does boil down to Rust or C++. This is a low-level tool, not a webapp.
Of course, Mercurial gives lie to this assumption.
What it matters is if it is fast enough for the use case being targeted.
As side note I remember when C compilers for home computers generated worser code than junior Assembly programmers.
It takes a lot more than a toolchain to write fast code.
Even then, Mercurial is implemented in Python and quite usable
The fact that a Java rewrite of git actually exists demonstrates the falsity of this statement.