Didnt he take a serious beating against Kimo? I know he locked him up at the end but I remember he could hardly stand and wasnt able to fight the last fight.
Your mostly right about them not knowing shit about submission defence but then there are guys like Ken Shamrock who knew a bit fighting the pancration stuff, and Oleg Taktarov knew some good sub defence.
I would counter your argument that while the opposition might be limited, Royce was limited also, whereas you have to think Vinny has trained wrestling, boxing and various other things a hell of a lot even if he does pull guard.
I understand that Royce was limited but you have to kind of bring it all together to become the best. It's the same reason that Rocky Marciano wouldnt be close to a world title in boxing now a days. The ga,me has changed and everyone has improved so much. Royce was a killer, but at the same time he was predictable and fight knowledge didnt show it yet. He flicks his leg and went for a takedown every time, and if he didnt get you down, he went on his back and easily kept his opponent on top of him. No one even knew how to stand up let alone out grapple him. A lot of the submissions Gracie locked in arent seen these days, and it's not because he was so good that he could lock them in, it's because his opponents couldnt avoid them. He submitted people with RNCs without sinking in his hooks, or even controlling the full back position. These days, people know enough to avoid getting choked out from what was basically a headlock, but back then they felt their throat closing and tapped out of fear.
Royce is amazing, and in terms of legacy and dominance he is one of the greatest of all time, but when you're talking skill level as an MMA fighter, I don't think he showed nearly enough to be considered one of the best by today's standards.
I'm not saying Vinny is one of the best either. I dont think he's shown enough against high level oposition in MMA yet and it'll be interesting to see how he progressed. Maia would probably be my pick, or Mir.