Yeah, but it doesn't cost much to accept connections on all ports (AIM did it in the 90s).
DPI should be able to easily detect and block non-DNS traffic on port 53, as well as IP over DNS. Just a matter of configuration effort; but lots of networks lack configuration effort, so it's worth a try.
5190 continued well into the 2000s.
5190 was the default port, but if it wasn't open, any other port would work. You could have the client do a scan to try ports until one worked.
It'd be fascinating to get an at-scale timeline of ports blocked from common client connection points.
I assume it's drifted over time, but couldn't guess which ways / why. (Other than converging on blocking all non-443)