Take for example your starting companion Kabb Uppercut, who starts the game out as a scoundrel. While that isn't a bad class, there isn't much synergy between Kabb's special uppercut ability and the rogue abilities. I could have turned Kabb into a soldier, getting the soldiers melee damage bonus for the uppercut. But instead I decided to turn him into an assault, as the uppercut's refund of AP works really well with the assault's repositioning game. I can turn Kabb into any of the 8 classes, and give him any of the 4 basic weapons, for a huge range of possibilities. And if I wanted, I could have him be a different class in every mission without the slightest disadvantage other than it being confusing to me. I can even get any focus points I specialized him with refunded anytime, and put them somewhere else. So if you and me both do some story mission with Hawk, Kabb, Trick, and Jae, we might be using completely different character classes and loadouts and have a very different experience.

On the negative side, if we both do the same story mission, it will be on exactly the same map. And any triggered events like reinforcements will happen with the same triggers, which can be time or some player action, like reaching an objective. And side missions can actually reuse maps you've already seen in a story mission. The semi-procedural map generation system of XCOM 2 does produce better map variety.

So we can summarize Star Wars Zero Company with having challenges that are relatively fixed, and solutions that are very flexible. With dialogue only happening at the base, there isn't really any practical difference between a companion and a freely created mercenary. It will be interesting to see how much replayability this system produces.