That sounds like an unwillingness to play Tactical on SM side, not an issue of Traitors Assaults being able to Cap.
Your playing the wrong game then mate. if you want kills and that's all go to call of duty or Halo. K/D ratios in this game doesn't matter(unless your trying to fill your ego). the only thing that matters is points and winning through team based play.
My only complaint with the shield bro right now is that the shield seems to protect them even if you outflank or shoot from an angle. They were described as a class where if you try to attack them head on, you're gonna have trouble, so you need to outmaneuver them. That works for me, but I've noticed lots of times when I am shooting them on the side that does NOT have the shield arm and I still get the indicator that they are taking reduced incoming damage. I don't know if this is a glitch or intended, but if I'm shooting the guy in the power pack on his back, his shield should not be helping him at all. For the record, I think it's a good class and am not crying nerf. I just think it should be changed so that shooting the SHIELD (and perhaps slightly around the shield, as there is supposed to be a power field) reduces damage, but being outflanked (shot from behind or from the sides) should do full damage.
The rumor of shields being OP has been dispelled by the devs with hard numbers in terms of total kills and deaths of the class... (I'm talking about last week's stream) What's funny is that those same stats also completely confirmed that the MoN was utterly broken right when the loyalists said it was, despite all the cries of "git gud" by the Chaos players and their assumed skill superiority.
LSM don't need a melee capper, they need more exclusive, ranged toys for their capping class to contrast with Chaos' capping class having access to melee weapons.
That being said, I won't be surprised at all if later in the game Tactical Marines can equip melee weapons instead of ranged. Would certainly make sense and would not be hard to implement. Exactly same principle as the Apothecary. If it turns out to be true, there ya go, melee capping class.
What matters to me is having fun. And I am having fun playing a meleeclass But, this isn't about me, this is about the playerbase at large and the game design. (Which is why I wrote the rest of the last post).
Honestly scouts would make so much sense here. They can cap (being Troops selections and all), they are squishy (in contrast to the MoN) and they are super long range (also in contrast to MoN).
Testing it also revealed that the shield, when broken, continues to block everything except plasma cannon shots with no negative impact to the ground assault at all other than he can't raise it. We broke a shield, then tested it by having him crouch (which completely covered his body with the unraised shield) and advance on a target. He was able to reliably advance into melee lunge range with all but the plasma cannon firing on him because the "broken" shield was still blocking everything, including a predator autocannon, multi-melta, and heavy bolter. Only time I killed him was when he advanced a little too far and I shot his backside as it poked out from behind the shield...which was done on accident when he was in melee range anyway so in a realistic situation I would have been dead already. Just because the stats say one thing doesn't mean that there isn't something wrong and there still is work to be done on...well everything really. Right now as far as I can tell that situation I just ranted about is the cause for a lot of "ShieldBro OP!" cries.