While this isn’t technically true, I can definitely see how this myth was formed. My father ran on a 486/66 with a modem from 1995-2001. In 2001 he got cable modem broadband, but his 486/66 was so slow that it couldn’t process complex web pages much quicker than it already was, so he saw no actual speed benefit. So he went back to the modem, at which point I almost lost it (“How can you want to go slower?!”)
Later he upgraded to a Pentium 3 @ 450MHz, and could finally perceive the modem as a bottleneck.
Ironically, two years later, I did the same type of thing (downgrade powerful hardware): Through a telephone conversation mix-up, I agreed to reserve and purchase a Yamaha snowblower — and when I got there, I had reserved the wrong one. What I thought was going to be a $600 18- or 24-inch blower was actually a $1300 36-inch semi-industrial model. I was coerced into buying it because renigging on the reservation meant I would be charged $50 because these things were in demand in the middle of winter. So I bought it to avoid the fee, took it home, opened the box, took one look at it and knew I could never use it for my tiny driveway without being embarrased (it wouldn’t even fit in my garage with both cars), and proceeded to box it up and return it. On that day, a snowstorm began. As I’m returning this monster snowblower, I get a goofy look from the kid helping me; when I inquire, he says, “I’ve just never seen anyone return a snowblower in the middle of a snow storm!”.