The fact that both Gurley and Chubb were so good does give credence to the "great OL" philosophy.
The Trent Richardson comparison may be good, as in 2010, when he was with Mark Ingram, Alabama had 4 future NFL starters on their offensive line.
I might be looking at some Georgia OL players if I were a GM.
There's plenty of reason to think Gurley and Chubb are special athletes independent of their team context. Both guys were clocked at around 10.70 in the 100m as high schoolers. That kind of speed is rare for anyone, but especially for two big power runners like these guys. Ingram and Lacy aren't nearly that fast or explosive. Richardson is a pretty great physical talent, but even he probably couldn't run with these two.
It's also worth pointing out that Chubb's freshman season was better than anything seen by any of those Alabama backs. He just did 1548 yards at 7.1 YPC. Ingram's best season was 1658 yards at 6.1 YPC. Richardson's best season was 1679 yards at 5.9 YPC. Lacy's best season was 1322 yards at 6.5 YPC. As good as those guys were, none of them were as good as Chubb. And we've only seen one season of Chubb. If he actually improves, it could be scary.
Beyond that, the "it's the system" scare tactic doesn't always work out. Sure, Alabama's friendly offense probably made Richardson and Ingram look a little better than they really were (though Ingram just finished a pretty decent season). I could just as easily point to the Miami teams of the early 00s for a counterargument. At one point in time they had Reggie Wayne, Santana Moss, and Andre Johnson at WR. They had Clinton Portis, Frank Gore, and Willis McGahee at RB. They had Jeremy Shockey and Kellen Winslow Jr. at TE. Just because a player's teammate is awesome doesn't mean that he isn't awesome too. For my money, Gurley and Chubb are first round talents who just happen to be on the same team. They're not creations of the system.
Bottom line is that every prospect is going to have his doubters. Reggie Bush did. Adrian Peterson did. Darren McFadden did. Knowshon Moreno did. Mark Ingram did. Trent Richardson did. You expect to get some pushback from the community, no matter how good the player actually is. What you have to ask yourself is whether or not the player in question is really legit. Personally, I don't see a flaw in Chubb's game. You name a quality and he has it. Vision. Balance. Agility. Speed. Power. Fast-twitch explosiveness. Character. Work ethic. Receiving skills.
Between high schoolers and college players, I look at probably 100+ players every year. Every time I turn over a new stone I hope to find an elite player, but the overwhelming majority of the time there is some glaring flaw that prevents me from going overboard with the hype. It probably happens 1-2 times per year that I see a player who instantly causes that "a-ha" moment. Chubb is one of those guys and if he can just stay healthy then I think we will see in due time that the skepticism isn't warranted with him. He ranks in the top 5-6 RB prospects that I've seen in the past decade.