Well yeah, because ControlPersist is just “make session creation fast” by multiplexing them over a single SSH tunnel. So you still have “ssh internal session creation” overhead but the tcp and ssh handshake is the slow part. The speed gap between pipelining with ControlPersist and Mitogen is small enough that it’s, to me, not worth the bugs and limitations of Mitogen.

I do get the annoyance of your script though.