[nat]

Is there any advantage/difference to using ProxyCommand with netcat vs just saying "ProxyJump bastion.example.com"?

[termie]

ProxyJump was added in OpenSSH 7.3 so systems from a few years ago might not support it. It does the same thing as ProxyCommand with -W %h:%p but you can’t set custom options for the jump connection with ProxyJump.

[stragies]

OpenSSH 7.3 was released on 2016-08-01, so more than 3 years ago. Nobody should be running SSH versions this old (hopefully).

[Pete_D]

CentOS 6 lives on in enterprise, unfortunately. (don't know exact OpenSSH version but didn't support -J when I checked earlier)