The more I have thought about it, the more I think the real answer for Terminators of all kinds (i.e. Heretic and Loyalist, character models and squads, etc.), is to increase their resistance to enemy "to Wound" rolls, which both is fluffy (representing their incredible durability) and a way to make them genuinely powerful on the tabletop.
My idea is that all Terminator models would get the following rule:
If an attack is made against a friendly model with this rule with an AP value of 0, then that attack has a -2 modifier to any of its "to Wound" rolls; If the attack has an AP value of -1 or -2, then the attack has a -1 modifier to any of its "to Wound" rolls; if the attack has an AP value of -3 or better, then there is no negative modifier to its "to Wound" rolls.
In practice, this would make Terminator models almost invincible against most AP 0 weapons (like Bolters, Lasguns, Pulse Rifles, Splinter Weapons, etc.), which would match the fluff, and much more survivable against "medium" AP weapons like Heavy Bolters, Autocannons, Krak Missiles, Battle Cannons, etc., which again is reflective of the fluff. This would also mean that you would have to really dedicate high AP attacks to deal with Terminators efficiently, in turn making them much more survivable the they currently are and increasing their in game value for holding objectives, absorbing enemy combat power, or just staying alive long enough to make an impact on the battle.
This rule could also be applied to all Land Raider variants, making them both more viable from a competitive angle and more true to their fluff.
Edited by L30n1d4s, 04 November 2018 - 10:27 PM.