Not sure if previously stated, I just think the problem is this:
A standard t1 army comp almost always has a few t1 arty in it. This is because t1 arty is good at both PD killing and as a combat unit. This means you almost always have t1 mobile arty available to kill PD that spring up. Its cheap and it works, and it helps to kill army units as well.
A standard t2 army comp usually does NOT include MML, as they are terrible combat units outside if niche situations. 99/100 times, you would rather have a few more t2 tanks to bolster up your forces. This means that once you see a firebase, you need to pause land facility, build 2-5 MML's, haul their ass too the front line, kill the PD, and then advance. By then, whatever reason the enemy built those T2 PD for already fulfilled their task (cover for an upgrade, secure reclaim field, buy time for t3 land). Now you are left with a dead firebase that already fulfilled its purpose, while you have a few MML's that will now do fuck all for your army.
I to fix your problem, I see two solutions: Make MML more of a combat unit (splash increase?) to have it be a standard part of a t2 army. This way you can counter t2 PD quicker/more effectively. Problem is this would wreck havoc with the meta and cause a few problems. Not sure if we want the game to go this way.
Make the missile damage significantly higher. This will mean you could kill t1/t2 PD much faster, with less units. Having a single MML in your army might be useful as a utility piece. Or rushing a pair of MML's out in a transport could actually break a firebase fairly quickly. Also this way, its interaction with TMD will remain unchanged.
Food for thought.