Can you please give a comic reference to these background below-deck crew members. Since they are 'all over the place' this should not be hard. However, I do not think they exist.
The fact that the guy from below decks was there hiding behind the doors - presumably watching the fight - seems to suggest that there aren't numerous superflous below-deckers he can join. In additionn the people whose task it is to defend the deck with alchemist fire are also all ordered below deck to fetch it up. Suggesting that there aren't a bunch of below-dfeckers who can fetch it up with her.
Although we do know that there were at least five below-deckers to join Ozzie and Carol, is not the fact that Ozzie needed to come down too suggest that there aren't that many. Who may perhaps be doing more urgent work to help against the giant problem than Andi trying to fix the impossible.
That's a lot of 'then' for one panel."Bandana finishes her yell and looks away, and extends a hand to point out the fins while continuing talking. Then Andi's expression changes from shock to fury "how dare she treat me as an erring subordinate and then stop paying attention to me" - then her arm begins to come up, as Bandana's words continue - then half-way through Bandana's speech about what to repair next, because Bandana isn't looking, Andi sees an opportunity to knock Bandana out, and takes it".
I think you are taking your soldier fantasies too far if you think reflexes only apply in combat situations. Even thinking that people need a 'drilled response' to - to chose the classic example - move their hand away when it touches the stove is comical.Reflex only applies in an actual combat situation - a drilled response - something physically lashing out at you and your combat-drilled responses kicking in.