You can't possibly justify this tactic.
What you do with your marines is you gives them mines and let them run around the map rampant in sneaky places where aliens would pass
Now your thinking 'WTH has this got to do with offensive mining?' Just hear me out.
While their carrying their mines, and happen to hear an Onos coming, they can plant a defensive line in front of them to help deal some damage to it.
Or if they going to siege, they use the mines as another defensive line to help deter off any incoming skulks without wasting bullets
Or even mine near alien RTs and shoot them a bit. You'll never know how many times the gorges on my team fell for that and tried to heal the RT only to step on a mine :O
I've had these tactic used against me, and I thought it would be worth sharing
And another tactic is to mine the hiveroom's floors randomly. You'll never know when a gorge runs rampant in a hiveroom
And f you could share....well....
The armory isn't broken, it's the players that are broken. And if you have a problem with humanity, you'll have to direct your ideas and suggestions to your deity of choice.