Unfortunately, at least for now, HP ice wont be the best against palkia, its water/dragons, so it isnt weak to ice. Air slash would be the better fast move. It likely will be more useful in PvP or if salamence dragonite and when it comes out, garchomp, are in gyms
It might not be the best for giratina, as it tends to carry ancient power, which togekiss is weak to, but it will be good against the other dragon claw carriers, in particular Dragonite and Flygon.
HP ice is i'd say the second best HP for dragon slaying (the best being dragon), and its still good as a tank counter for palkia as is.