Fire Emblem is the one of the only cases where I was never happy with DLC practices from Nintendo. I only played Awakening, and one bought one map in it. The one to farm money. It cost $2 or $3 for one map, but worse, I remember feeling like I needed it. Money was hard to come by, and that map was clearly designed to farm it. In my view that's poor DLC. And then I didn't buy Fates because I couldn't stand the expensive and confusing scheme of the three versions. By the time Echoes came out, I forgot all about Fire Emblem.
Now when I saw the Three Houses DLC, I thought that you got very little for $25. Maybe I'll be pleasantly surprised (or maybe I've been spoiled by Smash, Mario Kart, and Breath of the Wild), but I think I'll hold off on getting it for now. They need to earn it.