Luke has some of the best MMA-specific Jiu-Jitsu in the sport. He might have the best. I'm not saying that he is 'the best' BJJ guy out there - that is inaccurate when people like Jacare and Maia, not to mention plenty of others, are in play.
But Rockhold might well be the best in terms of effectively integrating BJJ techniques into MMA, and making use of them in an MMA fight. First, his mount is terrifying - let's be honest, he wrecked Weidman's career and ruined his chin. Secondly, his ability to snatch submissions, particularly from MMA-specific scrambles and openings, is astonishing.
It's just a shame that he seemed to lose his motivation of late. Frankly I don't blame him. Absolutely murders Weidman yet the UFC forces him to take an immediate rematch because Weidman was friendly with management and they wanted him to be the champion. Weidman then falls out, and he gets KO'd by Bisping in a shock upset. Out for a year with injury. Defeats Branch, and then gets KO'd by an absolute monster in Romero. Given his long absences due to injuries throughout his career, his interests outside of MMA, and the personal difficulties that led him to leave California, it's been a tough stretch for Luke. His technical deficiencies in terms of his hands, leaving his chin exposed, and only possessing rudimentary offensive (as opposed to sublime reactive) wrestling, have also become clearer and at his age it's difficult to see them being fixed.
Regardless of what happens in the Weidman rematch, Luke is secure as a great MW.