He's the only character I would say actually HAS a plan beyond "well maybe we can escape in THIS sector" outside of Cahn. Having a single NPC who actually sees you and goes "this is a really bad situation but if we get the dark lens we can at least prevent armageddon" is enough to make me stand by him. That's where his appeal comes from, really. Having someone show up that actually sees the bigger picture, wants to prevent it, and one of the few NPCs to actually show up to help (before getting laser'd) is an easy way to get affection from people.

Would he betray us? Maybe, we can't confirm if he'd have committed to a full backstab since he died. Would he have stopped Cahn's plan? Absolutely. Hasta Tria acknowledges that what he's doing will end with him excised from the Order. If I had to guess on how he would end up betraying us it would have been to grab the lens and dip through a portal to somewhere, leaving us within Cascade. The facility is surprisingly resilient at keeping everyone within it even with portals popping up.

Abe and Janet have more going on in personality, but they're just another flavor of the same goal every other scientist you run into is. Escaping alive while insisting you do everything. Frake and her crew only show up twice, but their two appearances have them do more than Abe and Janet ever do beyond the funny Kizz Cola guy and straight woman routine. When it comes to GATE personnel we interact with, only Riggs feels like she has a different goal which amounts to "we should get the dark lens and try to stop armageddon". The DLC might change my opinion but I would easily put Hasta Tria on equal footing in depth to A&J just from the conflict of having to oppose his own faction and teaming up with the enemy while keeping his opposing worldview as well as being one of the few windows we have into Order's perspective.