I think he deserves partial credit.
When he says that guys were diving on legs without control in the 90s, he's absolutely right...but that wasn't unique to legs. Back then nobody was talking about systems of minor control positions...for anything. Armbars were a hope and a prayer and a spin from mount. And since leglocks were exclusive to no-gi back then, it was doubly true, because the "no-gi is just scrambly and fast" narrative was gospel back then.
It's true that there wasn't much in the way of instructionals on leg control back then. Stephan Kesting's Kneebars and Roy Harris BJJ 101 Vol 3 are the first 2 I can think of that dedicated time to the minor control positions. I haven't had the pleasure of working with Stephan in person, but I can tell you that in 2003 I hosted a Roy Harris leglock seminar in which he focused on 4 minor control positions - controlling from them, flowing between them, and dealing with people who try to escape or counter. When I last asked him about it, Roy Harris said that the control positions he teaches are largely unchanged from the Sambo he learned. Personally, I feel I've seen him make some changes in emphasis over the years, to shore up some of the aspects where control is difficult, but that could also just be my subjective experience of it.
In the instructional world, Eddie Bravo probably deserves the credit for being first to show an entire series of minor control positions, and to make that the primary topic. His rubber guard laid a template for how to teach the entire path from major position to finish.
John definitely deserves credit for the level of his teaching, and for putting his systems onto film in an organized and thorough fashion. He is undeniably a major contributor. But there are plenty of other folks (far beyond the couple I've mentioned here) who deserve a share of the credit for the state of leglocks today.