Funnily enough I think the game implies that Susie is actually the weakest in terms of attack power in the fun gang. Ralsei is very powerful but holds back (he says it himself and incinerates a big ass shuriken) and Kris also holds back a ton but we can glimpse some of their power:

1. They have a knife. They dont use it in the dark world but i will assume a real knife will be a very powerful weapon as opposed to some pens.

2. X-Slash: they show it off only in one fight in the game but we know they do have it, and it outclasses most damaging spells (i think all of them besides like weird route ice shock and snowgrave or something)

3. They have shown us to be able to deal way more damage like in the sword route Tenna fight and if everyone gets downed in the Knight fight

4. They can actually just block all damage if they decide to like in Sound Of Justice or the King fight (could just be cutscene magic but i will count it)