Ben Eddy is right about the guard. Post 2007 ADCC and beyond was when you saw the level of guard play really start to keep rising and rising.
In no-gi too it's difficult to cleanly pass the guard and hold it for a few seconds. it can be done, but it's more difficult than without the gi. I feel really confident saying that some of the best guard players like Rafa Mendes or Joao Miyao will probably never get their guards passed in no-gi.
Watch Rafa, and elite passer, trying to pass Joao Miyao for 15 mins. At the time I remember being very surprised he wasn't able to do it. He comes close a couple of times bit never seals the deal
https://www.youtube.com/watch?v=9jPXPLEgAHc