I doubt it'd be all that influential. Nulling other weather and giving it Fire boost on top of Water immunity is really quite stellar, and it'd only be vulnerable to things like, say, Sandshrew and Drilbur as far as weaknesses go. However since it hardly provides team support, given the weather goes away upon switching out, outside of Stealth Rock, it'd really just act as a wall to blocking Chinchou. Though I'm not necessarily able to think of a scenario in which Chinchou is completely stunted dismantling a team... 9.9