To respond more throughly to the first post...
If you've played this game, you'd know that the hardest difficulty is basically impossible to beat without losing units - the Gaidens are to help you out when you inevitably lose them.
It's obvious that they made this game with the intention that it would be too hard to keep everyone alive; the gaidens, and also, the fact that when a character dies, its items return to the storage, for example.
Characters do have their own colours, just not to the extent that they have been in recent games.
...who replace characters who are defeated. Just don't use them if you don't want to...?
Again, not forced on you at all. Don't use it if you don't want to.
It's sad how much people complain when the game isn't a carbon copy of FE7 =/ People complained about different magic triangle in FE9, different supports in FE10, as well as the game being split in to parts (which FE7 was anyhow, lol), and now a few tweaked mechanics in this game as well. The game is largely unchanged on the whole, people just need to stop getting caught up on such minor details and play the damn game. <_<