Hes also talking about how the water is soo much improved compared to Miles and the remaster but fails to see that they where downgraded compared to the OG game.
Eh, I don't love the water effects of SM2 (it still needs a lot more incidental effects to round out the boxy spray when he waterskis or the limited interactivity when he floats, and I don't know if they're going to get all that in.) However, it's a disingenuous argument to throw around the "downgrade" term.
For one thing, the water effect change from SM1 to SM:R/MM was a choice of style, likely not a technical choice. One version of the water has a lot of choppy texture which looks nice at certain distances but breaks as a clear texture in other conditions; the other is more smooth and has bigger "waves" and avoids that moving-tinfoil look and repeats less, but it has less pleasing definition and doesn't have the busy churn of real water. In either case, the way the water is done is the same; they just changed the texture or normal map arrangement, and people might like one approach better than another but it doesn't seem that the change would have been done for any performance reason. You can see in each version that the system is same, just one looks one way and the other looks a different way.
Regardless, the actual DF discussion about water is the actual effects and how they upgraded the water's interactivity and simulation, which is inarguably an improvement over SM1. (Whether it's
enough of an improvement or if the improvements actually worked is debatable...) The water isn't just one basically flat surface in SM2 with some effects to make it look like it's moving, this new game has geometry changes and definition even when action is not splashing and churning it about. Watch the actual segment of the video, DF specifically talks about how the water is interactive, plus how it has a more consistent glossy look thanks to RT maintaining the reflections in ways that screenspace cannot do. You're looking at the similar churn texture of SM 2018 and SM2 versus the undulating texture of SM:MM, but it's the jetskis carving up waves in the background that DF is talking about being where the work went in.
There's not some never-before-seen next-gen water system here as far as I know (and even if it is doing anything new, the sum of the effects is not perfect,) but it simply and clearly is complex beyond what the developer used for water in the previous game.
(BTW, it kind of makes sense that they went back to a more churning surface texture this time, because now they have the geometry deformation ability to keep a consistent look close and far away.)