I wouldn’t try and look for a solid answer to what the heck is going on in our PvP matches.
League and similar ilk tried their damnest to make sense of their modes, only to please no one and scrap the whole thing.
The easiest conclusion is it’s rehearsals and military simulations. (In real time, not whatever Nova does with the Ops) An important detail is everyone we play as is a part of Ghalt’s BattleBorn initiative.
So there is a believable suspension of disbelief that Ghalt would have the BB do dry runs under different environments and objectives (maps and modes) to improve peer-to-peer relations between the members.
Answering why teams are mismatched outside of breaking the fourth-wall that a player (us) exists and chooses whoever.
The only problem with this, is time. As urgent as their mission is to save the universe, is it believable to think they’d waste so much time running combat routines endlessly? My answer to this, is that all PvP matches are post-Rendain.
This is what they’re doing to stay in tip-top form, as Ghalt sends small squadrons (why there’s only 10 characters practicing at any given time) to handle missions (previewed during the Heliophage epilogue).
This can answer why the LLC is allocating resources to this endeavor (the minions) a use for POWs (Thralls) and an excuse to retire old Sentry units via a brutal death (Think how Navy’s retire Battleships)
I think this explanation about sums up every plot hole our PvP matches do to the overall plot line, and addresses them in a plausible manner within the context of the overarching story.
So feel free to use this as your head canon going forward.