Man, the idea that ISDN was going to last 50 years has to be one of the bleakest Bellhead memes I think I've ever heard. "You will only have 144kbps and be happy."
The error was in not seeing packed switched networks as the clear winner not in choosing a modulation scheme that was designed to bring maximum bandwidth over existing copper infrastructure.
In any case, the strength was that you could bond up to 24 channels in a North American PRI package, which is what a lot of businesses considered their "T1" service, or used as a mixed group of DID and LOOP channels for calling.
Interestingly, in the end, they used bonded ADSL to provide an encapsulated 24 port PRI "circuit" to the customer using just 4 wires.