[Info] List of new Legacy Moves:

It's an odd move, but Rhydon has been semi-famous for being able to learn it in the main series games. They even made an anime episode about a surfing/swimming Rhydon.

A fire move would have been more useful vs grass types though.

long hair dont care gyarados ftw

Water Gun is 5 power and 5 energy in 0.5 seconds
Bubble is 12 power and 14 energy in 1.2 seconds
Waterfall is 16 power and 8 energy in 1.2 seconds

Over 6 seconds, that would mean each gives
Water Gun - 60 power, 60 energy
Bubble - 60 power, 70 energy
Waterfall - 80 power, 40 energy

To give a quick answer, one (simple) cycle with a hydro pump would be
Water Gun - Used 20 times for 100 power, 100 energy in 10 seconds plus 130 power in 3.3 seconds.
Bubble - Used 8 times (round up) for 100 power, 112 energy in 9.6 seconds plus 130 power in 3.3 seconds
Waterfall - Used 13 times for 208 power, 104 energy in 15.6 seconds plus 130 power in 3.3 seconds

Summary (pps is power per second and is roughly proportional, rounding/floor aside, to dps)
Water Gun - 230 power, 13.3 seconds -> 17.3 pps
Bubble - 230 power, 12.9 seconds -> 17.8 pps
Waterfall - 338 power, 18.9 seconds -> 21.7 pps

Rough numbers seem to show it is pretty good.

P.S. Excuse the excess math. I typed as I went.