These guys outsold the Beatles and the Rolling Stones at one point.
Yes they were just actors hired to work on a commercial sitcom, but nobody can say they didn't turn that opportunity into much more.
They didn't originally play their own instruments but it was their voices and with their songs being professionally written and choreographed their personal energy and group personality is what made the difference and turned them into a generational Icon.
Many of their songs are very good, even astounding given the circumstances. I think they deserve more legitimacy than they generally get.