That's because the Trygon is such a beast, a monster, a murder already. I mean really he's a Gargantuan Creature that was given better stats and put in for regular games.
The way I see it, I'd give the Maw-claws to the Tervigon and put it in midfield, a Winged Slayer Tyrant should get Ymgarl and be frontline heavy support, Prime should get Miasma and be rear guard (controlling and protecting the artilary of your chioce), and Trygon should get the Reaper and on challege duty.