I think the three big problems in his kit are:

• Lowest damage potential in the game. He needs damage buffing or armour removal
• Tentacles move enemies out of range, necessitating radial weapons (and making most of them significantly worse due to the length of the tentacles)
• THE CAST TIMES

Also a mild nuisance that Barrage essentially doesn't scale off range. The knockdown radius does but big whoop, that's not how you use it anyway.

I love Hydroid, and I have a hot take that he's really good for when you get him due to having what you need to clear the starchart in a really fun way, but by god the scaling on this poor frame is atrociously bad.

Anyway, some hopes:

Passive is some kind of damage buff or a loot buff.

Undertow and Tidal Surge are merged. New ability is a damage vulnerability or an armour strip. (I don't see them buffing Barrage given they completely passed over Corrosive Barrage previously, maybe for Helminth reasons.)

NO MORE CAST TIMES

Tentacles have damage transference a la Tornadoes, or at least don't lift enemies up in the air where you can't hit them. Suction effect so enemies actually get caught in them.

Tentacles scale off range or power strength, or at least spawn intelligently according to the navmesh so you don't get random wasted tentacles doing SFA.