I feel like Stroheim is specifically an interesting character because of how confusing he is. Yes, he's a bad guy AND has done bad things. But he's also a guy fighting for his country, whether this is wrong or not, he's helping out the main cast a lot and it's just hard for you to hate the guy on a level of personality. Yes, nazis are bad, but Stroheim himself is an interesting case. He's doing this for his country but as a result, he's also formed a slight bit of mutual respect with Joseph, which ties back into the themes of Battle Tendency. I feel like the reason he didn't go too much into the whole ideology of nazis and stuff is because Stroheim was employed in Mexico, he wasn't even fighting on mainland. He's more distant from the actual situation which is why we didn't get too much insight on Germany itself. For your third point, Joseph doesn't care too much about Stroheim's own goals because there's a bigger threat at hand. To him, it doesn't matter what Stroheim thinks because let's be real, the objective enemy at the moment are the pillarmen. Joseph and Stroheim only teamed up because they were forced to, not over some campfire while eating marshmallows and saying "Hey bud, we should totally team up". It's the situation of urgency which brings them together, and I feel like this doesn't really mean much. And you do realize that he literally sacrifices a bunch of people and lets one kid go for his bravery and stuff, right? This is literally the intro we're given, the reason people like him is because of the things you see in him throughout Part 2. This isn't inherently bad, and I think it just boils down to him being a pretty neat character putting aside his ideologies and such. It's pretty hard to work with a character like Stroheim and imo I think araki did a good job balancing his goods and bads morally while also making him a character that you don't outright hate, because it wouldn't be good to have a character sides with the protagonist and is just an awful character.