The historical significance of punk-rock — at least as much as it's defined by the modern version — has always been a matter of some conjecture, I think.
Depending on who you talk to, seventies punk bands like the Ramones, the Sex Pistols, and the Clash either saved rock and roll from its own excesses of the time, or just flat out destroyed rock altogether. Once again, depending on who you talk to, a decent argument could be made either way.
There is little doubt for example, that the biggest bands of the late seventies time period when the punks came along, had by and large become bloated by their own success and had generally lost touch with their audience and their own original ideals. Rock had become big business, and radio at the time in particular had become over-run by the relatively watered down, radio-safe fare of bands like Styx, Boston, and Foreigner.
As this argument goes, the Rolling Stones, for example, might not have ever made the stripped-down, back to basics album Some Girls, were it not for the influence of the punks. It's also a matter of record that people like the Who's Pete Townshend were also paying attention to bands like the Clash, who would eventually open for the Who on their 1982/83 stadium tour.
Change was in the wind, and people like Townshend and Jagger at least were smart enough to realize it, and get somewhat ahead of the curve.
On the other side of the coin, an equally compelling argument can be mounted that by drinking the whole back-to basics "D.I.Y." sort of Kool-Aid that was the punk-rock gospel, and by vilifying pretty much everything that came before it, punk-rock single-handedly laid waste to the whole idea of stretching musical and artistic boundaries.
For all of punk's somewhat justified (at least at the time) anger directed towards the pretentiousness of bands like Yes and Pink Floyd, the result of scaring away any future Jimi Hendrix from trying his hand at so much as an extended guitar solo, never should have been part of the deal. Not only that, but punk itself had no shortage of artists with lofty, artistic pretensions of their own (and I'm talking to you here, David Byrne).