Re: We shouldn't feel fine
You're broadly correct, but the specifics aren't:
"80s computers may be obsolete, but many of them still work."
In the sense that they turn on, maybe. But that's if you kept them in relatively good condition and kept the boot disks as well. If you didn't have all the parts in storage, they wouldn't work very well, and there are lots of pieces that wouldn't work. Try getting a computer to display anything if you didn't also keep a compatible analog TV, with either the right RF or analog input. Or to produce a disk if you didn't already have one.
"How many iPhone 13s will still work in 20, 30 years, even if it's just as an iPod because the phone functionality has moved on (for which Apple can't be blamed)?"
Basically the same amount. If you put it in storage, you can take it out in decades and turn it on and it will be sort of fine. The battery is the only part that is likely to die, and in twenty years it won't be in great condition, but it will still boot up. You will certainly have lots of problems with it, but they parallel the problems you would have with an 80s computer. You probably couldn't access Apple's app store, so you couldn't install things that weren't already installed, similar to how you couldn't easily load new software on an 80s computer without rebuilding the hardware to load it onto media. You could get the old XCode to run so you could build from source, but only if you're willing to virtualize the old Mac OS, just like you still can write in Z80 assembly and have that work. You probably couldn't buy replacement parts for your old phone, just like how you couldn't replace a chip on your 80s computer should it decide to release the magic smoke. In fact, if there's any difference that jumps out at me, it is that you have a greater chance of the magnetic storage from the 80s computer degrading without external damage than the flash in the relatively sealed phone, making the phone more likely to have the software it started with.
Phones don't last very long, and they're not designed to, but they would keep working if you preserved one. For the same reason, a lot of old computers didn't get preserved and ran their last halt instruction back in the decade when they were bought. Your preservation of 80s equipment doesn't make it particularly resilient.