Not so many artists with a 7-good-album back catalog (not few in number maybe, but few as a % of all artists) - though not as rare as those with more than 7, you're right!
Did the clash & the jam really release 7 good albums? Do you mean between them?
From my glass half-empty world view, a lot of bands fail to better their debut LP, and the vast majority of best work tends to be on 1st 3 albums.