Maybe damage is just too on/off.
What if, instead, the basic damage mechanic [this is a big change, but if its RIGHT, then bloody hells, GO FOR IT] happened to add, say, the weapon's DICE to Damage and Penetration for every DoS on the hit. his occurs up to twice, or once if firing in Semi or Fully automatic modes, and it takes two dice of accurate to count as one real die of damage for this mechanic. Obviously since tearing involves dropping a die, sorry, it don't help here.
So a Lasgun hitting by at least 2 DoS deals 1d10+5 Pen 2 as a base. Or could do up to three hits of 1d10+4 Pen 1.
A Long-Las could do, with a full accuracy bonus, 3d10+7 Pen 5. That's actually quite brutal [though two of those d10s do not generate RF]
A Vanquisher Round could be dishing out an additional +8/+8 on a max accuracy shot: Its base is three dice, after all. 5d10+18 Pen 24? I hear we'd been having problems with heavy frontal armor…
A Plasma weapon gets a special little kick-up, by increasing its bonuses thanks to the extra die in Maximal.
A Las Cannon… well that just kinda brutalizes crap now. I'd recommend lowering it by 1d10 if this change were to be done. A solid hit would thus result in 4d10+18 Pen 18
Melta Weapons would stay brutal. Just, slightly more so.
Worst Case scenario, if you want to help keep Las and SP competitive [since Rares of those two tend to be nowhere near as capable as even a Scarce of other types save low-tech], the basics and pistols could just add a +1/+1 to the final total whenever it gets boosted. Not quite like an extra die, but decent.
Tons of ways of doing things, really… But somehow I'm thinking that offshoots of the lightning claw rules might be a good middle-ground to "well we're going to have to make this melta"