Realistically, the 63A being weaker than the little 9mm ar15 is weird. It being a little weaker than the l85a2 and m16 makes sense, same rounds, shorter barrel. So the weird thing there is how strong the little 9mm ar15 is, ever since it was buffed a while back.
More important, gameplay, I think 25 damage is about right. It's still enough to achieve many of the same shots-to-kill on trash as our regular assault rifle damage of 30, but it's also enough weaker to hurt its performance against mid/big zeds, contributing (along with reloads and weight) to counterbalancing the excellent capacity, rate of fire, reserve ammo, and recoil, making a very unique balanced weapon.
Don't get me wrong, I think a stronger LMG could work too, but this loads-of-weak-bullets role is more interesting, and more fitting, since the LMG we've got is a shorty 5.56.
Commando will probably have to wait a while before getting any more content, but eventually maybe we'll get another LMG that better fits the heavier, stronger-per-shot role you hoped for. RPD comes to mind.
The SCAR and 63A should keep or expand the contrast that they have for variety's sake, I think.
SCAR has nice potential for mid/big zeds through DPS, so if the 63A needs to be made more appealing, rather than making it less special by boosting it to more standard damage, I think its potential for trash should be improved.
Penetration getting added to the 63A could do that. It wouldn't have to be a whole lot. A good starting point could be enough that a stalker/crawler/cyst (20 head health, 1.5x assault rifle damage vulnerability) behind a cyst/clot/slasher/siren (1 penetration resistance) barely gets 1shot decapitated with hollow point skill, but a slasher/clot (20 head health, no assault rifle damage vulnerability) behind one wouldn't. I'm not sure about my math, but I think a penetration score of 1.9 would do that.