Fortress Knight. That is all!
Nope I will not be promoting to Great Knight, that class is too close to being worth using lol. Besides while Master classes are technically higher tier, their stats aren't straight up superior, Advanced classes are plenty good enough to finish the game with.
Now Fortress Knight is the worst endgame level class period. Not because it's bad in the sense that it'll be much harder to beat the game or anything (it'll take longer, wont 1 turn any maps haha), it's simply outclassed by everything else. Like most classes, there's no objective reason to use it when Wyvern Master/Bow Knight/Dark Knight exist. What I actually mean by best team comp is that I'm even able to make this meme team. After all the best teams are the ones you enjoy using.
While I do think it's cool I can play the game like this, it's a bit of a double edged sword. The reason this is possible is due to the lack of specialization for a strategy game. For instance, in past Fire Emblems only specific units could use a bow making them anti-air specialist. In Three Houses, everyone can use a bow, so everyone can do anti-air. Doesn't help that bows are also OP as hell in this game, but I digress.
I'd love to see fully customizable teams return in future games, just next time maybe they make it necessary to create a diverse team. :L