i don't know, when i played DD in hard mode i always waited for the bubble to appear and ran over with slower people like warlock or summoners, when i tried to charge over, the water killed me pretty fast or other people died because of it. If you die to it with a low geared character its no wonder.
I dont think they increased the damage, thats just how it always was in hardmode, you just feel it more now because you play it with weak characters that would have never run hardmode otherwise.
Usually it is no problem to survive the water, use SS and some resist shield and movement speed buff, or if you have HM block also helps.
It is still a lot easier for new players now, all you need is one decent geared player in your group who can basically solo it (except for some mechanics)