>but Foo Fighters are mediocre and have persevered by merely
>writing decent, inoffensive, middle-of-the-road rock in an era
>when nobody seems to know how to do that any more.

They've written some very good songs in their lane; Long Road To Ruin, for example, is an excellent song, as is Pretender. Calling them "decent" is a smack in the face- to say nothing of the great songs that permeate their 90's output. I will say their albums as a whole have ranged from yes, decent, to very good, and IMO they've actually gotten better at crafting whole albums as time has gone on. IMO their singles output is excellent, though that lane may not be the most exciting.

>For me, Grohl's best post-Nirvana work has been popping up in
>odd session man type roles. He drummed on Killing Joke's
>self-titled CD in 2003 and it was monstrous. Probot was also
>a fun album though it didn't stick to my ribs as a Serious
>Metal Fan (tm).

Well This is a big part of his legacy though, isn't it? I don't think OP limited it to his "big two" output.