Ah yes, I remember it well; by 1973 I was in a BOAC Associated Company, which set up its computer reservation system piggy-backed onto the BA system.
A workstation appeared on my desk. I soon discovered that with my Supervisor log in I had not only the power to look at the reservation status of every sector of any service in the next 3 months, but that I could also type out a message to a friend, enter a 4-digit screen address, and send it to his screen where within milliseconds it would wipe what he was doing and show the message. This annoyed the hell out of recipients, but it pre-dated email by about 20 years and was quicker than Telex.
And yes, it was a "functionally difficult and illogical mess", so not a lot has changed.
Dear God, I'm drifting my own thread. Sorry, it's an age thing.