Do you assert that we had a good understanding of all of the problems that a computer could solve before making it? This seems absurd to me.

GPs point is that the technologies you've mentioned solved real problems before they were adapted for different use cases. They didn't make Darpanet and then think "man, if only there was some use for this" until the Internet came along. They designed it to send signals between distant nodes while being resilient to individual nodes being nuked.

Only after DARPAnet solved that problem did it get adapted to some other problems (ex: how do I send cat pictures to people)?

AI was developed with solid used cases - mostly image recognition or other classification problems. Remember when you couldn’t select text in an image file and paste it into a document? Well that’s a solved problem. The fact that AI has been overhyped and business struggle to find uses for it doesn’t diminish the cases where it does work well.

Fair. Maybe let’s look at it a different way. The computer is a solution to N known problems and M unknown problems at the time of creation. I’d say the N/M ratio is vanishing small.