Interacting with armor is neither inconsistent nor random...It like saying ATG are random and inconsistent because they have different penetration values.
Not causing engine damage at 75% or dying at 0 HP is an inconstancy and should be fixed.
ATGs are primarily interested in damaging units, and so interactions with unit armour make sense. Snares are not primarily a "damage dealer" ability, their main goal is to cause engine damage. This is made less consistent by the fact that they have a chance to deflect, which can cause them to sometimes not cause engine damage in the expected number of strikes. This part of the interaction doesn't add anything to the game.
The mechanics behind snares require that they cause damage, as being snared requires that a (medium or heavy) vehicle reach 75% health, but due to this they should not cause a random amount of damage.
If you can fathom a way to ensure that snares reliably cause engine damage in x number of strikes on a given vehicle regardless of whether they deflect or penetrate, then I'd be "happy" to see their penetration/deflection damage values stay as they are. I mean, if all you want is Allied snares to be weaker than Axis ones, then just have allied snares always do 80 damage, and Axis ones always do 100, making units with health equal to or greater than the panther more resistant to allied snares than equivalent allied ones are to Axis snares. Snares can be balanced differently without being random.
I still think all snares should be standardised, however. I really don't think there's any need at all for Allies to have weaker ones than the Axis.