A Barrett Light Fifty is not a LAG, it is a TL7 version of a TL5 Antitank rifle.
A current version of a LAG is available now. It is called the 20mm Neopup, can be shoulder-fired and will blow a hole the size of a basketball in the side of an oil barrel. Look it up on Youtube.
A basic suit of TL13 Battle Dress costs as much as an M1 Abrams Main Battle Tank.
A squad of Battle Dress equipped troops costs as much as a U.S. Army Tank Company.
A suit of battle dress can be taken down with an Autorifle (FN-FAL), an M60 Machinegun, an M2HB .50 cal Machingun (easily), a Barrett Light Fifty, a 40mm Grenade Launcher, a LAAW, a MAAW, and numerous other low-tech weapons. An M1 Tank won't be be seriously damaged by any of these weapons, an M2 Bradley or a Striker only has to be worried by a couple of them.
As long as it can be taken out with small arms, Battle Dress is an expensive joke. It's not worth the money, the training time, or the loss of the troops that were counting on it's protection.
There is no rule in that CSC that says you can wear light armour under Battle Dress. The rules on page 132 specifically say that you can't combine Vacc Suits, Combat Armour, or Battle Dress with other armour.
The example character I used was pretty typical of an ex-marine PC. The NPC bodyguard (ex-marine) on page 85 of the Core rulebook has STR 10, DEX 8, END 10, Gun Combat (Slug Rifle) 2, and has Combat Armour, and an ACR. I hadn't even considered that you would be attacking a Battle Dress equipped soldier with a Desk Clerk or some other type of REMF. If the Battle Dress equipped soldier has bonuses, ALL it means is whoever shoots first wins. The Battle Dress is just an expensive NBC suit.
I have used every weapon I listed above except the Barrett Light Fifty, plus quite a few I didn't list. I know reality, and I've played Traveller since about 1980. Combat Armour and Battle Dress never cost so much for so little benefit as in MGT. This is still the best version since CT (and is better in many ways), it just needs a little tweaking.