i'm jumping in because i get your argument of the clash's influence (and i know they influenced a lot!!) but....
say something happened and fall out boy ended up as the basis/big influence for basically every band from now on...would their "importance" make them good....no!
now that's a really dumb situation but i'm just saying, influence does not equal "everyone should like/respect/listen to them" type of stuff. i'm not completely discrediting them anymore (still haven't listened to London Calling) but just relax!
not everyone in the world actually likes the clash. so idk man. i mean tons of people hate modest mouse or pink floyd or led zeppelin or dinosaur jr or anything.
I fucking hate metal. But I sure admit that Black Sabbath, Metallica, Iron Maiden are historic bands, and don't deny their importance.
But why are they important, one might ask. It has to do with creativity, content, historical context, so forth.
I don't really dig Sex Pistols and The Ramones, but I consider them untouchables for what they did to punk. And I love The Clash because with London Calling they initiated the punk of the 80s, which is imo the best punk era.
So Foo Fighters, that band is bland, they just sound formulaic, it doesn't impress me. It is easy listening, only just a bit heavier. By easy listening I mean it isn't challenging, y'know, not challenging for the listener.