Crazy idea, let's make them work with their unique vet 3 benefit: The -50% ability cooldown reduction.
The cost of abilities are reduced by #%, # being a fair and balanced number.
The current cooldown reduction can be pretty nice, but ability cost is also a significant barrier to using abilities, so...let's make them work late-game through that. Can't win by shooting, win by grenades.
that doesn't sound like fun does it?