The lance was amazing for ceadeus, but every other weapon type is just as viable under water. I like how it made you learn new movesets for underwater battles, it keeps you on your toes and keeps the game fresh, which is awesome in a game you're going to put 999 hours into lol.
For the most part while it was amusing personally it was more of a slog to deal with the underwater elements. Though for that particular title it added something different to do within the same formula which is what made it unique.
This time around there are a bunch of new mechanics to be learned similar to what went on with the underwater battles. So will just have to see it as a movement in a different direction.
Perhaps after this title is over and feedback is gathered, they will reevaluate the decision to have removed underwater combat. Similar to how they brought the cats back due to the massive outcry for them. As it was a huge selling point for MHP2G. And seeing how they have injected steroids into that aspect of the game in 4, Id say they do take the feedback given by the majority seriously.
With that being said better pray there are others who like to turn blue underwater along side you make enough noise to see a potential comeback in a future version.