> and have major or glaring security issues
Telnet the protocol is secure if you either (a) use the Telnet ENCRYPTION option (such as with Kerberos ktelnet), or (b) run it over TLS (standard practice in IBM mainframe environments in which Telnet is still heavily used). Most Telnet clients and servers, this Python telnetlib included, never implemented either. But people present the protocol itself as being insecure, when it is just that the majority of implementations of it never bothered to implement the security extensions which have been defined for it. Telnet-over-TLS is just as secure as SSH. Telnet has the advantage of having various standardised extensions which don't exist in SSH, such as IBM 3270 and 5250 block mode terminal support, the SUPDUP protocol used by PDP-10s and Lisp Machines, serial port control (enabling you to configure baud rate/parity bits/etc if you Telnet to a serial port server), and Kermit. Now, you may not use any of those features – in which case SSH will suit you perfectly fine – but some people do. And, in principle someone could define equivalent extensions to SSH, but by and large nobody has done so, and even if somebody did, they wouldn't be standard so little or no software would support them.