i just read the patch notes and it seems like the heavy strikedown is being adjusted to deal more damage, i think, but the lights are still strictly worse than the vanguards in every single way.
this should 100% be changed, everyone can agree on this. strikedowns are supposed to be low cleave, high damage compared to vangaurds which are supposed to be high cleave, decent damage.
Those attack names are arbitrary labels and have nothing to do with the actual stats. There are plenty of nonsensical damage numbers across many weapons, such as axe “heavy” attacks doing less damage to maniacs compared to light swipes.
iirc vangard (cleave) dmg is also shared between the targets so it’s more overall dmg but less dmg per ennemi hit.
those numer also depend on weapon modifier for cleave and 1st target