Although, these would-be changes are far more appealing than current Hydroid we have, it feels....rather underwhelming. Feeling that Hydroid has much better potential that is not being utilized fully. So, personally, I would add these:
-Enemies that have their armor removed by Plunder or enemies with no armor in-range of Plunder take extra damage, correlating to how much damage boost you get from Plunder
-Tentacles passively draining the armor and shields of enemies they're holding and if they have no armor, drains their health, giving it to Hydroid (and maybe teammates)
-Casting Plunder while Tentacle Swarm is active to empower them, draining armor, shield and health at double the rate
-Casting Tidal Surge while Tentacle Swarm is active to bundle all held enemies into Tidal Surge and after the ability is over, they're held down by the tentacles
-Tentacle Swarm having "head" to shoot at, to spread the damage out to all enemies held by the tentacles or targeting them one by one, dealing extra damage to them or shooting an enemy held by tentacle spreading the damage to other held enemies (similar to zephyr 4)
Still, I am just glad that my boy Hydroid is finally getting proper rework.