There is a lot of discussion about this topic. At this point, it is pretty much a consense that T, U and L are sets 100% worth it to invest some time learning if you are really willing to get faster at 3x3, at least at some point. The other sets I see some more debate arround them, specially H...
Imagine that WCA keeps operating eternally. Do you think that there would be a point where no more WR would be broken, and people would just compete for big titles?