I'm not sure if ksmbd still makes all that much sense. A user-space daemon can saturate almost any network link using a single CPU core. And the attack surface... if you control ksmbd, you immediately own the machine.
Not 200Gbps of 16kB block writes, that's for sure.
Agree with you on the rest about kernel vs userspace, just taking issue with the bit about a single CPU core.
The link will be whatever the fastest network port you can get on an apple machine is. Its not 200Gbps - the apple end will be the limiting factor. A single core can probably fill that just fine.
And being pedantic - 200Gbps links are not a significant percentage of installed network ports in the computers in the world... so "almost any" is pretty accurate.
Certainly not a guarantee at today's link speeds. We're increasingly leaning into RDMA and other forms of offloading for a reason.