"McCartney...never excercised quality control" I think a large part of the problem was that Lennon & McCartney were each other's quality control.McCartney's best post-split songs have been every bit as melodic as before but trite lyrics have been the rule rather than the exception.
Lennon's 'seventies output retained his capacity for perceptive &/or biting &/or witty lyrics but,all too frequently,these came trapped inside unimaginative & unadventurous melody lines (his weakness for overproduction didn't help either)
To redress the balance I would suggest none of the following would disgrace any record collection:
Lennon:John Lennon/Plastic Ono Band,Imagine,Rock 'n' Roll
McCartney:Band On The Run,Run Devil Run
Harrison:All Things Must Pass,Brainwashed.