Not a hydroid main but I am kinda sad when seeing undertow go. There are a bajillion of tweaks that makes undertow useful while "being less annoying". You could make it so that enemies got corrosive proc'd when affected by undertow. You could make it so that when teammate shoot the puddle it counts as headshots (a bit like mag's 2).
This is the example of a "useful but generic" warframe. If you are to make an armor health tank who could proc corrosive, saryn and tank frames who subsumed hydroid's 1 could do the job. You CAN'T tell those people who don't play hydroid to play it with this kit. Don't get me wrong, I agree that hydroid is significantly stronger than what he was before. However I also agree that Hydroid lost his iconic ability and he isn't that special among all other cc frames.
Also with the logic that "stationary gameplay = less fun", I should prepare for the rework of Mesa's 4 or Nyx's 4, to name a few abilities out there