With the vitalis pet, specifically, it does reward skill to some extent. After all, you'll only get a Vitalis if you get drops at Vorago, which means you have to have a good DPS rotation or be a good tank.
Except it doesn't. On my own team, we have a particular person who is the best DPSer out of us all, on most days. We happened to get a Vitalis pet, but for some reason it went to another DPS'er who clearly got less (and admitted to this) XP than the best DPS'er, wasn't basing, hadn't Voked, and it wasn't Scop. We often joke on our team how our best DPS'er got sniped.
The fact of the matter is that drop rate for Vitalis is so ridiculously low, that you could win 99.9% of the drops for your roll, but the one time you don't get a drop, or a particular phase, that could be the one time the Vitalis drops and it goes to someone else. After all, no one gets drops 100% of the time. And there are countless stories of this. People who have consistently been doing Rago since it came out and obviously know the roles and how to perform them excellently, practically in the thousands of kills, have no Vitalis, saw maybe one, and it went to someone else. Then there are other people, who did a minimal number of kills at most, have poor Vorago experience and kills, but happened to get it by pure fluke.