this happened to me so I'm just going to post this but not sure if anyone else agrees with what I'm going to say. But I had 2 fire mages and 1 fire killer then I made a water support character after the fires got to a decent lvl. I was giving my water the cows and they kept leaving so for a while I never gave her a cow because they kept leaving but I didn't notice any difference in the amount of exp everyone got. The exp was the same when my lvl 90 water hybrid was bursting with them and my new water mage was bursting without a cow. That was a long time ago though since my water is now lvl 143 and lvled past all my fires XD I don't have any screen shots of the exp or pets but it did happen. So I don't think you have to have a pet for the water. It's a good idea to have a pet for the water for max exp but I don't think it makes a huge difference in the exp. That's just my opinion though. sorry if no one agrees with me...

I did not notice any difference in whether or not my water had a pet. It seemed to be the same EXP for everyone, once I stopped attacking with my water. I used 2 fires with low level pets and the water simply casted buff/debuffs.

The expected results have been achieved, not as impressive as one might like, but achieved.