you just need to use it right.
It has the same range as the spec ops snipe attack. My advice is firstly make sure it has recharged... it has a very long recharge - in my estimation it's about every third fight. The way to use it to maximum benefit is to use it as an opening attack.
First, Move all your men as far away from the enemy spawn as possible, then use the built in basic pet command of "attack my target" - it's the symbol with the target icon on it.
If you are at far enough range, spec ops will snipe and commando will use the rocket. select an enemy in the middle of the spawn to get the maximum from the area of effect.
Basically, it seems like you are just setting your men to goto aggressive which means they all attack random targets (this is useful for getting aggro away from squishies but not so good for precision attacks)
Learn how to position your men more and you will become a better mastermind.
Well no thats not what im doing i always attack at range and i dont think i need to be a better mm dont think im that bad now thanks i know where all the "attack my target" icons are 
The tactics you have said are of course correct and that not what im saying, i feel the lrm is underpowered and there is little control over it, there should be some kind of indication that its almost recharged so you can get into the right postion to use it and not have your commando use it when he feels like it and kill some random low lvl minion.
You can have control over it. If you position the commando properly before giving the order to attack, he will always use LRM when it is recharged.
If you think it might be recharged and you dont want him to use it, use goto to put him closer to the enemies. He wont use it unless he is at long range.
I agree it would be nice if you could see when it was recharged but as to being underpowered I disagree - it does huge damage and knockback in a big area of effect. It can totally destroy an entire spawn, especially followed by multiple full autos.
Ok now it may just be me but i find this power a total let down, my commando always seems to fire it at low lvl minion and even then it doesnt seem to do much damage at all.
I know the lrm can be a great power i mean it seems to work well on the epic power pool for blasters but for the merc mm set it seems under powered and is always fired of at the wrong time.
Maybe they could give us more controle over this power by adding it as a power option or at least give it a faster recharge or make it more powerfull.