ive noticed that iron golens can kill the dragons very easy, please, buff dragon life or resistence.

I can't say for sure whether it will happen, but I can say that's a pretty huge buff to the dragons' stats.

Mob stats in vanilla Minecraft is all over the place, in my opinion.

But even with that said, I feel the dragons stats are in a good spot at the moment, including health values. Different breeds differ in stats, but that is where they shine.