You are partially correct . The root of the real problem is very poor operation design. EC was designed much better in comparison to SnV and TFB. EC did a better job of rewarding a mixed group composition of ranged and melee, single target and aoe dmg. HM SnV and TFB are currently designed so that melee is just as good as ranged dps and there is little need for aoe dps. There is no reason for HM SnV and TFB to take any other class than the pure raw best dps class (assuming same gear/skill of course). Mara is at least very competitive for being at the near the top of the dps charts. In addition, it can boost the entire group's dps with no downside. In addition, a group can stack 4 mara's with no real downside and a significant dps boost. There is no reason in the current HM SnV and TFB to take anything else. The devs could redesign the fights completely to fix the issue, or they could add global cooldown to maras. It is highly unlikely they would actually redesign the operations. The alternative is pretty simple, put bloodthirst on a global cooldown. The cooldown could even be set to allow for 1-2 maras to still be 100% effective and only discourage stacking 3-4 maras.
Whoa! Because you feel the operations are poorly designed, your solution is to make changes to the AC's!? Yeah, ok. Next Maras will be complaining because their utility in the other fights (where it was fine) has been nerfed. Big picture dude, think big picture.