This is so weird to me. You cannot get Silver Snow instead of Black Eagles. Silver Snow IS Black Eagles. It is the route those characters were clearly conceived and designed for. These characters feel desperately out of place in Crimson Flower. Characters like Linhardt, a pacifist, or Petra, a hostage, or Dorothea, who seems confused as to why she's even there. Silver Snow is the route where you build a strong connection to edelgard and Hubert and that connection takes center stage throughout the war phase, which you fight alongside the Black Eagles. It was advertised.
Frankly, I wish people would stop saying "church route." It's the Black Eagles route.
If there is one canon route in this game... it's silver snow. It answers everything, it has the biggest set pieces, it is the most all encompassing without leaving major plot points unfinished, and it has what was clearly intended to be the games true final boss. It's not my favourite route. (azure moon for life.) But it's a total shame that people are playing the less coherent VW and CF routes and avoiding this one.