How much of "Poseidon" is really "stolen" exactly? I say just the title track and "Pictures of a City" (ok that's 16 minutes out of a 40 minute album but still just 2 cuts). Some say "Cadence & Cascade" is a "Moonchild" or "Talk To The Wind" retread but I call bullshit- it's a great original melody with some nice pseudo-romantic groupie-themed lyrics. The melody is also arguably better than the original melody, which was eventually reused for "Flight of the Ibis" on the "McDonald & Giles" album.
As for the others listed, I think "A Quick One" is about the equal of The Who's debut but maybe I'm alone on that. Shit, on a good day I prefer it. Sure, the debut has "My Generation" which is obviously one of their best songs but aside from singles "The Kid's Are Alright" and "Legal Matter" (which are both pretty lightweight IMO), most of it is energetic but forgettable British Invasion. Not all tracks on "A Quick One" work but they're generally more interesting/memorable (in fact the only one I'd really call lame is Daltrey's). And "White Light/White Heat"? Not as good as the debut but pretty damn close.