A heavy weapon kill should heal drastically less compared to a primary or special weapon kill! Force the invaders to use different guns than just their bloody heavy ammo!
Edit: The reason is simple. Heavy weapons kill a lot easier than a special or primary weapon. No matter if Gambit or Crucible. Players should be rewarded the most for playing the least easiest way. Not for playing the easiest.
Stuff ain't fun as it is now. Stormchaser getting 2-3 kills and healing the Primeval fully is just not fun to play against.