"Outdated" is a reasonable moniker for devices that accept cleartext telnet over the open Internet. That you can retrofit security onto telnet by running it over a TLS tunnel is not especially relevant, nor does it make telnet less outdated; secure devices are better off just using SSH.

What makes a protocol outdated? I would argue that outdated protocols "bake in" outdated assumptions. The telnet protocol has a builtin assumption that the network is secure, while newer protocols for remote administration lack this assumption and assume an actively malicious network.