well Oga is the de facto leader, but that doesn't make the rest "subs" .. it makes the bonds stronger if anything .. and it's Beel too, not just Oga, Beel & Aoi are pretty close as well (though that doesn't really work for the guys
)
and yeah, they do need that power-up it seems, why not, the enemies and Oga himself are using those powers
Aois loss was at least partially emotionally influenced too .. sure she got beat up at first, but only lost for good when she didn't even bother blocking Ringos slash to finish her off
& we know that she can be emotionally fragile at times
__________________
When we hunt, we kill
No one is safe
Nothing is sacred
We are Blackwatch
We are the last line of defense
We will burn our own to hold the red line, it is the last line to ever hold