I like Nakanos ending since well, like Kas, it still somewhat loops back to us the Champion. The reason why he is able to help beat the demons is because of our influence. And It is pretty nicely written, has nice arc to it, and it is something else compared to your usual enslavement.
And besides, I just like to think of the endings as non canon what if scenarios. But still keeping it somewhat consistant with the lore/characterization. Like, yeah, Kas does love us in her own twisted way. It is shown in the story multiply times. She probably wants us to prove ourselves so that we could rule next to her. But if we fail, she can just make us her own willing servent. Same way that it shows that Nakano could probably change his stance on us, but it would take time. And that he is able to reach greater highs.
And as for those not being "bad endings". I mean, yeah, not every bad ending is going to involve same, dour outcomes. It would be kind of be boring. For example, in stuff like Hirrud and Nakano , they just straight up kill us. Depends on what you find worse, enslavement or death, those could be seen as worse ones. And even best cases of enslavement are still bad compared to literarly being a free man/woman that is able to do things how they see fit.
Now as for them showing that someone else can beat Kas. I am personally not fan of idea of us being destined/only ones that can win against her. Kinda sucks the life out of the adventure, since we are
predeterminent to face her. Non of this is the choice our champion makes. And well, it does kind of invalid (more than others) a lot of other ending that I find sweet. Especially Arona and Berwyn bad ends. Since we can not really have our happy enslavement if no one else can defeat her. So yes, while it does undervalue our champion involvement in this demon problem, I kind of prefer it that way. And besides, it is already undermined considering that Kas is letting us to keep our soul to begin with.
Like, now whatever we accomplish is not because the desteny demands it. It is because we want to do it.
As I said, he only helps beat the demons. Nowhere does it say he is only reason they lost, or that he killed Kas personally.
Act 2 could realistically go on for a few areas (areas = new locations), possibly more than TITS. But the question is, are savin and his cohorts really willing to continue the story or will it prematurely end, as with TITS and the whole "Oh its 10 planets" just kidding fuck off you get 5?
Eh, to early to tell. This game just entered its third year, and well, we are just getting Khor minos update during/after the summer. So lets wait and see how big that moo City ends up being.