The Beatles are one of the most cited influences on the development of progressive rock.
Yes, and that was all going on around the same time. That dosen't strip The Beatles of any originality, they had that to spare. OMG they took ideas from other banRAB?
Because thats unacceptable. Sure its not at all common for all banRAB to do that. Surely it isn't.
You take ideas from your influences, thats normal for any artist. The Beatles took their influences ranging from rock n roll to pop to psychedelic rock and made something out of it.
Sgt Peppers and Magical Mystery Tour may have taken ideas from the psychedelic rock movement, but the end result was not psychedelic rock, it was something different. Those albums along with Freak Out, Days of Future Past and Tommy really laid out the blueprints for the genre of prog.
And that on its own, is an original idea.
I'm afraid you're wrong. I would cite a lot of examples but I'm about to leave soon, maybe later.