Hmmm... that's true. Being weak to magic/poison, both Rex and Indomitable make good candidates for the first boss to kill, so grabbing their trophies can be needlessly difficult at times. In the case of Labyrinth, you really don't have the luxury of choosing which boss to fight first since exploration is at such a premium. Itsaama as a weakener and Evolvia as a teleporter, however, will almost always be your second kill, so that's not an issue with them.
That said, I'm loving the gold infusion that the first boss gives you. It really lets you go on a shopping spree for the end-game. Namtar's first two forms also drop gold now, so the difficulty of Namtar's Lair isn't quite as high as it used to be (still screams "play as a Warlord!" though, since CYDSTEPP is the only attack that doesn't get gimped by at least one of his forms)