FWIW on Emscripten I specifically pick the slow-but-small emmalloc instead of the fast-but-big jemalloc because a small size matters more than performance in that case. My C code also rarely heap-allocates, and the few heap-allocations that happen are all in the init-phase, not in the hot path - e.g. even in multithreaded code, the MUSL allocator would be totally fine.
Performance in edge-cases by far isn't the only metric that matters for allocators.
FWIW on Emscripten I specifically pick the slow-but-small emmalloc instead of the fast-but-big jemalloc because a small size matters more than performance in that case. My C code also rarely heap-allocates, and the few heap-allocations that happen are all in the init-phase, not in the hot path - e.g. even in multithreaded code, the MUSL allocator would be totally fine.
Performance in edge-cases by far isn't the only metric that matters for allocators.