My 12 year old son just got into 90s music and the Foo Fighters are one of the bands he likes
I like some of their songs and think Dave Grohl is a cool guy who doesn't take himself too seriously
My son likes for he and I to listen to music together, including the Foo Fighters (recently in the form of the FF channel on Sirius/XM)
Anything that doesn't harm anyone else and brings a father and son closer together can't suck
Carry on with your subjective rage...
Furthermore, I would hypothesize that FF's longevity has directly led to Nirvana's continuing influence and popularity. They have been around 25 years and are still semi-relevant at this time. Someone just getting interested in music hears one of their "formulaic" songs and decides to research them a little. Oh, Dave Grohl was also part of something called Nirvana? What was that? Oh, Wow! Kurt Cobain was awesome! He was influential in alternative and grunge? What was that? Wow! AiC, STP, Soundgarden, Pearl Jam, etc. are great... I'm sure the Foo Fighters are much more effective in adding people to the Alternative/Nirvana/Kurt Cobain fold than pretentious Cobain worshippers on the internet.