Memory copying is on the order of 100 gigabytes per second. You can do 80 full payload copys and still out-pace a dog-slow 10 gigabit per second connection. If your bottleneck is memory copying you are either doing something very wrong and doing way too many copys or congratulations you have implemented one of the fastest network stacks.
Supervisor calls are also very fast, on the order of 100 ns up to maybe 1 us with all the Spectre mitigations. Even if you did something as stupid as one supervisor call per packet, you would still be getting on the order of 10 Gbps at the long end there and 100 Gbps at the short end. Which, again, means congratulations are in order because you have implemented one of the fastest network stacks. If you do batching and add just 10 us (us, not ms) of latency then that entire cost is so small as to be irrelevant. You are going to bottleneck on your memory copying first.
Network stacks are so slow almost entirely due to poor protocol design and poor protocol implementation. Usually both.