2 of the most common offensive types, with one apparently "broken". Most of their individual weaknesses are countered by the other typing Only has one weakness and that is a rare type.
Has to be a reason why Kingdra is the only thing Clair has that is remotely threatening.
I think it's been established that combos with only one weakness and few resistances isn't actually a contender for "best."
Water/Dragon is only weak to Dragon however it only resists Fire, Water, and Steel. So it can be hit for neutral by most things. However, offensively it has neutral coverage on mostly everything except Ferrothorn and Empoleon I believe.
It's a good typing but not really the best. --- I'm not against religion. I'm against all bad ideas, held for bad reasons, prompting bad behavior.