Eric Johnson (former Radio Promotions Director Remote Engineer at CBS (1990-2002)) replies ...
Of course he was....Someone once asked if JPJ was, to paraphrase, "the weakest talent in the band" at which point Page just laughed at the foolishness of the statement and said "go sober up sometime and have another listen" and he continued with "Jonesy definitely has his moments". John Paul Jones was and is a very solid bassman and part of one of the best rhythm sections in rock. He also had arguably some of the more interesting bass lines ever played for blues based rock. Consider that Zep for all intentions was a three piece band with a singer and Bonzo was not a guy for playing standard drum parts.
Remember also that Jonesy was also the band's keyboard player and in being such he was also the band's arranger on a good deal of what they played. Actually JPJ was likely the most musically trained of the band. Page knew him from back when he and Jones were go to studio session players when they met. JPJ was a choice that Page made for the band.
Try to keep in mind that there wasn't anything that sounded really anything like what they were doing. Even those that want to say they were lifting songs from the old blues guys have to admit that their interpretations weren't like anything done before them. That sound was original. And Jones was an integral part of that sound.
Then there is that thing that takes place when the right players happen to find each other and then that truly new and exciting thing/sound happens that's bigger than just the sum of the parts/players… that's when every member and what they bring to the band is integral and equally needed for the end result. It wouldn't have been what Led Zeppelin was or became without the unique talent and input of each one of those musicians at that point in time. So yes John Paul Jones was definitely an accepted member of Led Zeppelin....and as I said an integral one...as were each of them.