The Thief trait provides 25% stealth, -2 speed. Lise always seems to start with this trait.
Infiltrator passively provides 25% stealth, and the Infiltrator gear provides 50% more (10% head, 20% torso, 20% legs). With the Thief trait, this is 100% stealth.
With the Thief trait, an Infiltrator in infiltrator armor is undetectable (except by mist). This seems pretty overpowered (though given the difficulty scaling, almost necessary). Basically I have a group of Thief Infiltrators that can’t be targeted by anything besides Chiron artillery as long as they don’t get hit by mist. It’s hard to imagine this is intended, though it certainly makes capturing enemies pretty easy.
Not to mention that Infiltrator level 7 skill doubles all damage while undetected…which is all the time with 100% stealth, making any other build pointless. A single Thief Infiltrator can solo almost any mission barring too many Chirons or just a ridiculous amount of mist generators.