The problem with the Heavy NLRM Carrier, as I see it, is that while it might have Hardened Armor, it's still only got 10 tons of it, which doesn't make for terribly impressive protection on a unit its size. It might get an extra round or two of life, and the added resistance to TACs is always nice for a vehicle, but it's still fairly fragile and not going to live long once enemies get close enough for the NLRMs' reduced minimum range to matter.