Power armor would be good but only in niche roles... First off the cost would make it impractical for every infantryman. Second, it'd be big and bulky; not good for snipers or people that need to get in and out unseen or unheard.
Third, weight and logistics... Helo's have enough trouble moving 'unpowered' infantrymen to and from the battlefield. Armor would only add weight. Plus, spare parts and repair equipment would be a nightmare. We don't know yet how much trouble theyd' be to fix in a hurry, or what parts will break faster than others, and so on and so forth.
If anything, soldiers in powered armor would be a niche infantry-MOS; likely carrying heavier weapons like machine guns, and anti-tank weapons. Possibly comm gear and medical equipment. Everybody else gets standard issue stuff.