"but they really aren't the most important rock act in the last 15 years."
Yeah they are. That's not to say they're as good as the other bands you listed (cus they're not), but had Ween and The Flaming Lips never existed (god forbid!) I don't think the modern music scene would really look all that different. Radiohead on the other hand, launched an entire generation of followers, and I don't see their influence letting up any time soon.