If you've got const 6, for =<5 W, they're W2. If you're willing to splash... 35, iirc? W on one, or happen to have a omni/elemental booster sitting around, they're now W3, and can forge robes of the sea. Suddenly they're 20 water gems or less from being W3,* which means wave breakers, various summons (including naiad warriors or naiads if they're one of the N randoms, which means either pretty alright awe troops or a better platform to boost higher into water magics), Voice of Tiamat (at W2, even), most of the workhorse combat water magic, rain if you're looking to screw over a fire nation, so on, so forth. Just by their lonesome they can forge water rings, frost brands (!), water lenses (to give the boosted ones or other water casters free combat gems), rings of water breathing if you need 'em. Give 'em that ring and they can make boots of quickness -- suddenly those worst researchers in the game are a cheap and easy means of forging a good 2/7th of a solid SC/thug's loadout, and if you're having assassin problems (or want to make assassin problem for someone else
) they can pump out bottles of living water to help with that.
... so yeah, they're shitty researchers. They're also W1, and water is one of the easiest paths in the game to boost up if you've got that initial caster and enough construction, as well as having a few rather nice trinkets and whatnot. It's pretty much always fairly useful to have access to water casters, regardless of their strength, if you've got the W income to do something with it. It's better to have W2, obviously enough, but W1 can do in a pinch (or if you've got a limited amount of higher level water mages, due to events or whatev') and they're pretty good workhorse mages regardless. Just... yeah, don't leave them researching if you can avoid it :V
*Also you've got at least 1 W4 caster, which gives you access to, uh. Almost every pure water combat spell.