Anon, it's time to accept that the average chuuba IQ doesn't reach the triple digits. They are funny, charismatic and likable girls (aside from Kiara), but the vast majority of them aren't really that much into videogames like someone on /v/ would.
You got some exceptions like Korone, but most of them only play current year trending games, if they play videogames on their spare time at all.
They simply aren't going to play something like EU4 for 2 reasons:
1. It requires them to think, which they will find boring after a short while. Any game that's even moderately difficult is a problem because the whole point of gameplay streams is to give the chuuba something to do while she's talking with chat. Watching the chuuba lose and get frustrated is only funny in quick paced skill-based games like Getting over it, not on slow paced strategy or tactics based games like Total war.
2. Most of their audience isn't that deep into videogames either. They want to see their oshi play something that they have also played, so vtubers are encouraged to play something that's popular with the normies if they want to have decent numbers and audience engagement.
If you want to see what happens when a vtuber streams a game nobody cares about then look at Anya.
Slow paced games work best if they are so slow that it's possible for the vtuber to play them alongside chat. This is why something like Risu playing Va11-Hall A works perfectly.
If you want them to play something more mature and engaging try getting them to play Suzerain, though I'm not sure if management would allow them to.
Alternatively try getting them to play roguelikes, a genre which on paper seems perfectly suited for stream format but which for some reason I haven't seen a lot of them play. Imho it would be extremely fun to see my oshi play Noita. Spelunky would also work well with the more casual ones.
Not saying that chuuba's should only play whatever is most popular atm (I discovered Baba is You through one of Haato's streams and I loved it), but don't be surprised if they choose to play what everyone else is playing and is proven to engage the audience.
