(It's strange but whilst making this post I've realised how few Normal types there are in OU! Maybe they aren't as strong as I thought...)
Actually with eviolite chansey can take hits alot better than blissey. And also I think you mean porygon Z? Cuz in terms of sheer power porygon-z is by far mone of the most heavy hitting normal type with tri attack/hyper beam, a single nasty plot boost, along with its adaptability abillity. Ursaring being a physical yet slower equivilant.
A few of previous OU contending normal types moved down to UU on the generation shift. Such as Snorlax, and Togekiss. I also beleive stoutland was OU for a short time before he moved down.