I disagree on both counts.
Prime S-Jax had more yards from scrimmage than damn near everyone. When he had a good offensive line, he was the best running back in football not named LT. With a bad one, with no weapon around but him, even with injuries, he was still a 1,000 rushing yard running back who was an elite pass-catcher and pass-blocker. Gurley at his best was amazing, but when he had nothing around but him, he struggled mightily. S-Jax would still be a 1,000 rushing yard running back behind any line; I can't say that for Gurley. And I may be a S-Jax homer, but I wouldn't take him or Gurley over Dickerson and Faulk.
As for offensive lines? Between 2007-2012, we had offensive O-lines. Like, we sucked, not just because of injury, but even with healthy offensive lines. We were playing names like Jacob Bell, Jason Brown, Adam Goldberg, Brett Romburg, Mark Setterstrom, Claude Terrell, Jason Smith, etc. We SUCKED back then. This offensive line is just decimated. The ones we had in the past were decimated AND they sucked elephant balls.