I'd like to consider a possible alternative approach to Noburi's OP-ness, for sake of different angles:
Noburi has been growing up wrong.
By growing up I mean he was close to a puberty equivalent of Wakahisa. If he stayed with his clan, they would teach him how to train properly, or maybe take certain drugs or perform certain practices so his fragile system won't go off whack.
Wakahisa modify their chakra system in a pretty dramatic way (they literally put some of their magic organs
in a barrel). It would seem logical for this to have some
long-term consequences on their health, especially if left unchecked. I mean, Mori use a nihilistic mind demon to freeze their brains to ice, so that they can think in nice, orderly grids- yet even they don't modify themselves
permanently.
Noburi's superb abilities could actually come from that very problem- think of a valve. When Noburi tries to suck chakra from water around him he
opens this valve. He did it many times and trained a lot, so he's very good at opening it wider and keeping it open.
The disadvantage coming from that is that he'd be pretty bad at
closing it.
When Noburi sucks chakra through his tendrils, he's connecting water from his barrel to water around him. There's a force that's sucking chakra in, a difference in pressure, etc.. But when Noburi doesn't use his abilities actively, does the connection from barrel to water around end? Does his valve close naturally?
It's my suggestion that Noburi has a
loose chakra hole, so he has a problem keeping it in, especially in water.
It could manifest itself in him quickly losing chakra when he's in water, or a hit to his chakra capacity (since he can't hold it in), or even form a more general sickness that he has to figure out and cure in order to survive.
Just imagine other Wakahisa, when seeing his OP abilities, will actually
pity him, because he's doing it wrong, harming himself for quick power boost.
It would make him less of a special snowflake, and highlight the fact that he lacks the support and know-how of the rest of his clan.
Also it's more evil and real-life kind of dramatic.