I think they didn't have the long jump because the pack could be used to get the same distance. However, I would love the long jump back, because of the crazy platforming that can be gained from long jump and then water pack game play.
Actually, I am not a big fan of the game play the water pack allowed, but not the water pack itself. I like my Mario hitting and punching things, and picking items up and such. A jet pack power up for a 3D Mario would in my opinion be better...or a suit that does the same function. Maybe a revised Winded Hat or revised Raccoon tail with this additional game play element.