Tim Brown.
Ok, hear me out before you mash the downvote button.
Brown retired as the third all-time leading receiver with 1,094 receptions for 14,934 yards, and 100 touchdowns. At the time he also ranked fifth in career combined net yardage with 19,682 yards. Brown is the only player ever to retire in the NFL’s top five leaders for both receiving and return yards. And that’s after suffering a catastrophic knee injury and missing his entire sophomore year.
But now, consider who he had at QB. Yes, he had NFL MVP Rich Gannon toward the end of his career. But before that, he had a litany of failure at the position – from Vince Evans to Todd Marinovich to Jay Schroeder to Billy Joe Hobert to David Klingler to Don Hollas to Wade Wilson to Bobby Hoying to Marques Tuiasosopo to Rick Mirer to Tee Martin to Rob Johnson to a washed-up Brad Johnson to Chris Simms etc etc etc. The BEST of the non-Gannon litany was probably Jeff Hostetler.
(Contrast this to Jerry Rice, who went from Joe Montana to Steve Young to Steve Bono (good player) to Jeff Garcia to Rich Gannon.)
OK, maybe I’m misinterpreting the question. I was taking it as “best player on bad teams”?