The flak is an AoE weapon that is meant to deal high damage like a grenade. If I understand its topic correectly, the suggestee wants the flak turrets to be super effective on melee units and units that can roam through shields, like infiltrators, Vamps, and cutlasses. Because those units swarm in close-knit groups, flak makes a great last turret wall to have in and around a forcefield.
With that said, I looked at this list of suggestions, and like them all.