They could balance it with the space wolf literally taking up 2 or 3 party slots.
in the battlemap he literally does take up 4 squares. Although, you can see the party screen with him in it, and theres still 6 party members.
The sanctioned psyker and navigator could in theory match a space marine in "power level". although obviously in different ways, not a 1:1. marine being neigh impervious to damage, super strong, super fast, super hearing, etc. but pyskers could throw fireballs, teleports, destroy minds in large aoes etc.. depending on their specific skills. psykers ability to do large scale damage before or after demonic takeover is what makes them scary.
1:1 the space marine would usually win. but again, depending on their specific skills a psyker taking out a marine is not out of the question.
"romance" the title cards in the vid listed sexual preference of the characters.
"Sister Argenta" Romantic Preference: n/a
Its also balanced on support. the tech preist. support. buffs/debuffs. the cold trader. support. the more human power level people are support.
The sister of battle versus the space wolf is probably the only real direct power level issue. what could she possibly do to justify her position over him? (I think they are making the space wolf use melee exclusive. so she'll probably use bolters)
