Hello John
Telnet can indeed be useful to test the state of TCP ports on remote devices. More detail on how this can be achieved can be found at this NetworkLessons note.
Unfortunately, SSH does not respond in the same way as Telnet, so it cannot be used to test ports in the same way. This simply has to do with the way in which Telnet and SSH have been designed, and what kind of responses and prompts are actually displayed in the CLI under various circumstances.
Note that the Telnet protocol is not designed for this, but it is simply “good luck” that engineers decided to make Telnet respond the way it does, so it can be helpful in this way.
I hope this has been helpful!
Laz