Your idea, though nice Magnas, would lead once again to an endless balancing between pets. In that case, it would be better to keep the 4 pets as they are and try to balance them again, rather than doing it all over from the beginning.
Idea to make just one tank and one dps pet (but with 3 different skins) isn't a bad one. At least, it gives some time to later come back to it. Or pets stay the way they are right now (not really fully balanced) and Vaion comes back to it when he has more time (in another life!).
In any case, it shows how difficult it is to balance just four pets. I can only imagine how to balance class compared to... Firenze for example. It's like riding a dead horse ! Pointless !