Initially I expected that by the end of the game I would have some characters that were vastly better than others as you would find in Fire Emblem or other similar games however the developer, desunoya, has done a good job crafting characters that all fit a certain role in the party and even toward the end are relatively similarly powered. Even Sho who is definitely the weakest and most difficult character to level is useful as he is the only one who can open chests.

The level cap looks to be 40 but I was unable to get all of the characters to that level so here's the stats for everyone (except Rolenson) at level 29 which everyone did manage to reach. Rolenson is an exception because there isn't really a way to level him since he is strictly used to move units around and has no way to attack.

Furthermore most levels allow you to use all of your units so you won't need to pick only the best characters when going into a battle but it is highly recommended not to let anyone fall in battle if you're playing on hard as it will make the next level harder since the character has to sit out.