That might or might not be true in the real world. Often in my applications I'm creating at startup and then referencing later.

Still a custom map that allocated a bunch of nodes would be a useful optimization.

Actually it really depends, because allocators can also be kind of smart (and you don't have to use the default allocator).

And then, on the other hand - I really doubt GP's map beats a vector, with all of those pointers bins and stuff, in a non-contrived benchmark with 10 elements.

Finally - it's not either-or: There are better hash maps whose memory is sequentially allocated and/or are otherwise cache-aware. And there are data structures geared towards parallel execution on multiple threads; and towards SIMD; etc. etc.