Ranger Pets
The other solution is making rangers and pets immune from each taking damage from the same source (i.e. each taking damage from a single greatsword swing).
This is a great idea, I wish they made pets more useful all together though. When you are pvping the pet should be a threat to an enemy, right now people just ignore the pet and go straight to killing you making it useless.
More teams would want rangers on their team if players “feared” the insane damage or survivability that pets have.
I think most players would balk at the idea of sharing a health pool with an AI. Heck, I have played games where I shared one with a human and felt like punching them :P A separate health bar seems fine, particularly with the pet-swap mechanic they have given us.
Immunity to AoE would be a perfect PvE solution, but I am sure there would be PvP complaints. Not taking damage from the same source would not address the issue at all; pets die quickly (or instantly) to attacks that do not hit the Ranger because the player was able to dodge them. An AI capable of dodging these telegraphed attacks would be the ideal solution, but I am not sure how difficult it would be (not an AI programmer, so it is easy for me to say).