I've been in the Nether quite a bit recently, and I've noticed that Netherhounds are very fast. I'm not sure if they were recently buffed, but they seem faster than I remember. So the problem with them being this fast is that they lag quite a bit. I have a good computer too (over 100 fps average), but they move almost like teleporting robots. Them being hard to hit is a good thing, for sure. If the speed was nerfed, they'd be relatively easy to kill, so a health buff wouldn't be the worst thing in the world... Let me know what you think.
I wouldn't exactly nerf it, because there are ways to kill them without them touching you. Maybe a way to reduce the lag would be more beneficial. I am used to playing at an average of 15 FPS on a good day, so I am used to the lag. The downside to this is, I can't tell the difference. Would it help if instead of the immediate "Netherhound Howls for assistance," maybe do something that says, "You hear a demonic barking in the distance." That way, the players know that the nether hounds are close by, and then when the "howls for assistance" notification comes up, they know the hounds are close. It would be helpful to turn down the speed a bit, and gives s higher chance for survival among new players.