if u look at their solo careers, paul has so much oddball shit. he took some serious u-turns in his music. some of it worked, some of it was completely disastrous, but it was always unpreditable.
lennon solo stuff is downright conservative in style besides the odd avant garde piece of shit he'd do with yoko. but in terms of his solo records most of them were either stripped down singer/songwriter stuff or bland rock n roll.
even the harry nilsson album he produced was one of nilsson's most boring, disappointing albums.
i'd imagine if he hadn't been killed, lennon would've became an even bigger embarrsament than he was throughout the 70s.