If I remember right you only get sun damage on level 4 of vampirism in Oblivion, they can make it like that. But I don't know I don't play vampire much.
In Oblivion, you took zero Sundamage at Stage 1.
S2 - 1 Hitpoint per second
S3 - 4 HPS
S4 - 8 HPS
That was better than a slight reduction in stats and no regain. Some would argue that we shouldn't even have regain in Skyrim in the first place. Just by wearing a few enchanted items will completely negate those...minor drawbacks.