I'm playing pokemon right now out of boredom and I'm wondering why almost all Legendaries are incredibly easy to ko

Almost all the legendaries are easy to kill but right now I'm playing pokemon omega ruby which is a pain in the ass! First I have to capture rayquazza without killing him then after that this girl battles me with five of her pokemon and before I have time to save I have to battle Deoxy. I've had to redo this entire process 5 times since Deoxy is so easy to kill and I still haven't caught him yet I'm taking a break from it because of how annoyed it's making me.

Which Pokemon game?