Ability tooltips do not say whether they deal reduced damage to objectives or not.

[wanderdl]

I dont even remember what deals half to buildings... Warden Ult, Bebop Ult, Pulse Grenades, ????

 

[barlakopofai]

As far as I'm aware it's always been exclusively spirit damage. So pure damage and physical damage are not reduced after the natural damage mitigation wears off