nope. There isn't other solution that I can see to balance this atm. Maybe there is, it probably requires re-work of the mod's difficulty system. Player's weapon upgrades are too powerful & hard to balance.
- I have bump enemy defense. Otherwise, uranium rounds tears any powerful unit like butter.
- Enemy's damage can not be too high. Otherwise, they tear your defense like butter.
This results enemy units have very tough defense and deal small amout of damage.
When FFA enable, imagine dealing 10 damage per attack on a 10000 HP unit. They take forever to kill eat other. The enemy units also spawn fast from unit spawners. Your map ended up with never ending amount of units whom are trying to kill each other. That can bring your computer to a halt before the game starts. So the easiest way to balance it is to bump enemy damage and player entity health while enemy's health stay the same.
What I can do is to give additional buff for the healing items, and total shield value in FFA, using the same multiplier. That's about it.
I recall SpaceEx disables player's health regeneration. So you only rely on medpack to regen health.