If you can Power up for its second attack, though, a 2HKO is very easily done with a few Cherrims in play. Attack with its second attack on the first turn for 70 (let's say you have one Cherrim in play) and then on the second turn, attach a PlusPower or use Buck's and do 50 for the Knock Out. Healing 50 is a bonus.
Dialga G isn't going back to the Bench easily, either. You have to have a Switch/WP on hand to do so, and even then you can send it back up the next turn for a KO.