At the time that was a common statement, but I fail to see why X25 mandates dumb terminals.
However a profound difference was that X25 used streams whereas TCP uses packets. A stream is akin to a TCP socket.
It is a fundamental difference that stems from the fact that a X25 data exchange is safe from errors.
x.25 had a MFT (Metric Fuck Ton) of error checking (at each layer). I used to work in OSI based networking - debugging OSI issues was an art - no wireshark back then
However You could do some cool things with osi based networking binary attachments natively supported, years before the internet had it.
Interworking between legacy system like Telex, I used to have my own telex number and answerback and could have had an x.400 email address at the country level.
Ps id take site you linked with pinch of salt no mention of PAD's for example.
There was a smart gateway node that translated complex x25 from the Minitel service providers nodes into simple bidirectional stream of bytes to the Minitels, it was a specialized type of packet asssembler disassembled (PAD) called a PAD Videotex (PAVI).
Now x25 did have packets, Minitel terminals did not. So the PAVI and x25 servers were working very differently and with more complexity (hence smart) than Minitel serial terminals (hence dumb).
It’s not that x25 mandated dumb terminals.
Are there any public x.25 networks still operating?
Not that I know of. My plan if to use old line simulators and other tools i can find on ebay and telcom equipment reseller sites to create a "fake" private one. This is one of those projects that I'm working on purely out of novelty interest :P.
X.25 is a “packet-switched” “connection-oriented” protocol.
[which p.s. makes sense for traditional telecom’s view of the world, which as you know is circuit-switched. One of the main beefs of telcos in regards to IP was traffic management. Compare X.25 congestion management with IP. ]
Some kind soul has delved into the details of modalities of networking protocols:
One road not taken could have been to define a structured document format in ASN.1 that would be displayed by the terminal.