No, compared to not doing so many allocations that freeing them is time consuming or expensive. Having allocations slow a program down means that there are way too many, probably due to being too granular and being in a hot loop. On top of that it means everything is a pointer and that lack of locality will slow things down even further. The difference between allocating many millions of objects and chasing their pointers and doing a single allocation of a vector and running through that can easily be 100x faster.

Probably? Locality becomes fairly important at scale. That’s why there’s a strong preference for array-based data structures in high-performance code.

If I was them I’d be using OCaml to build up functional “kernels” which could be run in a way that requires zero allocation. Then you dispatch requests to these kernels and let the fast modern generational GC clean up the minor cost of dispatching: most of the work happens in the zero-allocation kernels.