The real problem lies in that there are very few facts and a whole lot of opinions that people try to rationalize and make them sound important by siting influence, sales and popularity. The three you mentioned, Fugazi, Sonic Youth and the Pixies are in fact highly regarded by many people. But from what I have briefly listened to, none of them do anything for me, but that's just me. I agree that it's easy to get trapped into thinking that all of the good music was done in the 60's and 70's as far as rock, because honestly everything that came out after 1975 was essentially previous music reworked in some form, but that's not to say that it should be discounted. Now if you were arguing originality it might be different.