The bigger point here is mortars has changed the game type Breakthrough enough to suggest EA needs to address this in some way.
The whole point of the game type is objective attack and defend with real confines on where all the players can be, all stands to reason of course but someone(s) just sitting back dropping mortars on objective zones in attack or on defense changes things.
If EA does not care then so be it, but odds are people will play the game type differently over one change. Mortars, something is fundamentally wrong with that unless EA intended it. Frustration with mortar attacks or counter-attacks may not matter to EA. Then do what others suggest with your own counter mortar, fire and move frequently and see if the game rebalances.