What does stand the test of time even mean in this case? People still listen to both Radiohead and the Beatles and lesser known "alternative" acts from the 1960s like the velvet underground today. All went on to influence others. I'd say they all stood the test of time. Stuff like record sales depends a lot more on how well your label commercialized you versus your musicianship. The mid century media era was also much smaller in terms of competing artists that were actually put in front of listeners. 3 stations on TV, a few radio stations playing music from the same record labels, a shop in town selling records from a few major labels, and that's all the discovery you have. popular acts were far more popular proportionally than popular acts in later years, just because you didn't have much option or choice otherwise back then.
It means that the Beatles (who the parent mentioned explicitly as a basic formulaic rock in contrast to the "peak" from the '90s) is much more well known now than Radiohead, and could even have been more popular than Radiohead even during the peak of Radiohead's popularity (with the general audience, of course). I doubt that the problem of alternative bands was media exposure, because they had plenty in their heyday. The issue is that their music appeal only to a small(ish) subset of people, and that most people would like something else. I don't mean this as a bad thing. It is what it is, but I find amusing how cultish their following is :)
