Comment by adwn
You're losing sight of the full picture: This "optimization" was such a hindrance that they had to rewrite the compiler before they could work on the ecosystem of their new language. From kristoff_it's comment [1]:
> When I first joined the Zig project, Zig was still using the bootstrap compiler written in C++ that would not free memory (it took more than 4GB to compile the Zig compiler). Some people at the time were asking us to prioritize work on the package manager but Andrew rightfully wanted to prioritize rewriting the compiler instead. In hindsight this was the obviously right decision: a package manager implies that one can very easily add an order of magnitude more code to their project, stressing the performance of the compiler. If we had not prioritized core infrastructure over giving people what they wanted faster, today we would have people complaining that adding a single dependency to their project makes the build impossible to complete.
> they had to rewrite the compiler before they could work on the ecosystem of their new language.
I think you may have missed that the intention was always to rewrite the compiler to become self hosted. Improving the C++ implementation any more would've been pointless optimization.