Almost everything is deadly to low armored, low DB creatures
Just joking, of course, but IMHO "balanced" doesn't mean that everyone should always have the same chances in everything at any moment.
Could such a character kill 4 ligthly armored foes in a single round?
Obviously yes, but again I see no problems with that. Dealing with similar foes is that character's specialization. It's what he spent half (or more) his DPs for. It's his moment to shine!
Put him against 4 heavy armored, parrying opponents, and his chances drop drastically.
Against 4 archers at range his 4 melee attacks/rounds will be useless (and yes, ammunitions run out, but a skilled archer need a single arrow to score an E crit).
Calming is a 2nd level spell, Sleep is 1st level. Even 1st level characters can safely cast them without having to worry about using up all their PPs and aren't restricted in any manner (unless, say, you ban or restrict magic in your campaign, but that's another matter).
What I mean is: yes, that character is going to be very effective at killing certain enemies. No, that's not unbalanced, because it's a very situational set of skills, that's not going to work everytime, is not going to solve all the problems the character will encounter and requires a lot of effort and DPs expense.