MTE is not about typed memory. It's for detecting invalid memory accesses outside of an object or outside of the lifetime of the object in general. hardened_malloc is the main place GrapheneOS implements MTE for userspace. In the kernel, it's implemented in various allocators and in Chromium in PartitionAlloc. The kernel and PartitionAlloc allocators have typed allocator designed unlike malloc. It's still possible to do partitioning for malloc via size classes and call locations.

Yes, this is exactly what you're missing and why what Apple has done is novel. They've combined MTE with typed allocators to reduce the performance impact and make it effective as Android failed to do.