Hi !
The current major issue with random sPvP is X vs X-1 (5 vs 4 usually) where no auto-balancing is done.
IMHO, for the duration of the “X vs X-1” match, the X players team may have a malus or the X-1 players team get a bonuses.
Some ideas that could balance these phases :
X players team can’t get any point by killing an opponent player.
X players team have 10% less health.
X players team can’t respawn until one of them died (making the match a X-1 vs X-1)
X players team respawn slower
X-1 players team have 10% more health
X-1 players respawn faster
X-1 players respawn with a 10s speed buff