Incorrect, and that was exactly my point

This is like saying that if the fruit at a store is rotten sometimes, it's not the grocer's fault, because the fruit had to come a long way and went bad in transit. The exact job you are paying the ISP for, is to deal with the hops and give you good internet. It's actually a lot easier at the trunk level (because the pipes are bigger and more reliable and there are more of them / more redundancy and predictability and they get more attention.)

I won't say there isn't some isolated exception, but in reality it's a small small small minority of the time. Take an internet connection that's having difficulty getting the advertised speed and run mtr or something, and I can almost guarantee that you'll find that the problem is near one or the other of the ends where there's only one pipe and maybe it's having hardware trouble or individually underprovisioned or something.

Actually Verizon deliberately underprovisioning Netflix is the exception that proves the rule -- that was a case where it actually was an upstream pipe that wasn't big enough to carry all the needed traffic, but it was perfectly visible to them and they could easily have solved it if they wanted to, and chose not to, and the result was visibly different from normal internet performance in almost any other case.