For my job I had the opportunity to work with quite some OSI standards on top of TCP/IP (X.216, X.227 and X.500, X.400 as application layers). My experience is quite in line with the common critique: most of these standards add more overhead than they're worth. It was also quite hard to bend these protocols into our use case (when bandwidth comes at a premium, it doesn't take long before the customer starts complaining).

I don't really see how a "dumb terminal" is a noteworthy feature of OSI? That's essentially what telnet does, and it too can just piggyback on top of TCP (probably the only protocol that makes use of all TCP flags available).