Armors lend themselves to special ops operations, taking out enemy government, espionage and such. Energy weapons are very useful and important, yes, but armor gives more tactical mobility. I don't doubt SA's ability to kick Batarian ass in war. I want to give them options that make such war unnecessary. To allow more tactical options. Also, protecting our people is more important than killing the enemy.
You do realize that you are starting to grasp at straws for any excuse why ground combat is relevant?
Our Legionaires can do SpeCOps just fine. Nevermind that the Batarians are a case where the government isn't the problem, but the entire culture.
Taking out the leadership just produces a Weimar situation as the rest of the upper castes resent the humiliation and we get another war when the Reapers come (when else would they do it?). Grinding them into the dust, utterly, means we can dictate how society is rebuilt.
Nevermind that in order to reach the planets, we have to wreck their navy first. And unless you want to bleed hulls, energy weapons are the way to utterly dominate that theatre. If we control space, we also control the ground situation as we can just flood areas with drones, break any resistance and redeploy the drones.
The Mk. II is at the moment just a shiny gimmick that doesn't really changes the battlefield situation in time to be relevant as we can't churn out millions of them (neither could the SA really pay for it that quickly) nor can the troops be trained fast enough in their use.
Miniaturized Energy Weapons on the other hand just amplify an existing technology to a level where more weapons can be mounted. The relevant training already exists but still means that the Batarians biggest threat is neutered. They can't strike back without a navy, after all. That means the SA can just besiege their planets and defeat them in detail at leisure.
Edit:
Sabotage then. Mk 2 is good for covert insertions, for operating behind enemy lines, for extraction, for sabotage of naval installations, for urban warfare.
Besides, again, protecting our people is more important then harming their people in my book. Thus, armor first, personal energy weapons second (ie next quarter).
You do realize that our people are on the ships as well, and there we have no convenient drone hordes to take the bulk of the casualities?
Making the ships that much stronger means we take away the Batarians ability to strike at human civilians.