I'd have said Green Day were a pretty key band in the late 80s/early 90s American punk revival scene. That scene was different to the more hardcore scene that was prevalent up to that time, but still very much a punk scene. Some bands bridged the gap, as will always be the case, Operation Ivy were part of the Hardcore scene but slotted into that Revival scene when they morphed into Rancid, Bad Religion were part of both too, along with others. Rancids Hellcat Records and Bad Religions Epitaph launched countless other punk revival bands, along with NOFX's Fat Wreck Chords. Green Day got popular, signed with a major and went for the money, and who can blame them?
There's many different areas of punk and little point arguing what's punk or not.