Xcom is turning into a bit of stylistic soup with this expansion. Moreso than it already was in Xcom 2.
IMO Jake Solomon's attitude towards Xcom is that he's translating a super generic FPS corridor shooter like Halo or the near-future CoD games, into a TBS. So it makes sense that we would have what are pretty much Destiny classes in this game. I think the idea is that the base game explored the clean and futuristic ADVENT a lot, now we're visiting the post apocalyptic stylings of the resistance. The only thing I'd say as that we're crossing the streams a bit, the Chosen aliens are somewhat Mass Effect which fits with the alien's style but they also have a bit of Predator in them which is much more human in Xcom 2 terms. Meanwhile the resistance factions themselves are too futuristic stylistically to fit with the resistance as we understand it, particularly the Templars. On the bright side they are exploring interesting themes, with the exception of the Reapers which seem like a mashup of existing classes.
This expansion seems like a trial run for mechanics to use in Xcom 3. I said a long time ago in this thread that I think the weaker enemies in Xcom 3 should move in small squads to emphasize how badass your soldiers and the main aliens are. It looks like the Lost are going to be a test of that principle, in a safe way where if its not a fun mechanic it won't hurt the rest of the game. I also think that they've realized the difficulty curve in both newcom games was awful and they're trying to fix it. The alien card deck system and rulers both look like failed attempts. I think the Chosen are a test run of a system to have individual aliens levelup alongside the player soldiers. My guess is that if the Chosen and Lost are popular, in Xcom 3 they won't be secondary game mechanics but rather a core part of how the alien enemies function.