You could only display it for researched enemies. I think that is doable and would not be cheaty. The point is to hide the math from the player. Think Blowpipe vs Osiron Security. Another example: Self Charging Laspistol vs Mechtoid. Takes a lot of shots, but you can kill a Mechtoid with that.
Then it's not cheaty but Friendly Tell-You-All Advisor, which is also bad. The player should get info about weapons damage, but come on. I'd feel insulted as a player if the game was so forthcoming. I want my math in the game, thank you.
Also, there is problem with 'what research?'. In Piratez, you usually have to research the corpse to get resses, but sometimes corpse is shared, and you need to research live enemy.
I'd be happy if there was a "target analyzer" function available to enable in Mind Probe type items, which will display you sort of a fake armor entry for the enemy, with their paperdoll, weapon(s) held, and armor values AND resistances (maybe resistances only in broad terms, like 'immune', 'very resistant' (1-20%), 'resistant' (21-70%), 'normal' (71-110), 'susceptible' (111+).
Displaying damage ranges would tell you nothing, since both Gaussian double-dice, and UFO single-dice have the exact same ranges while differing very substantially in the chance for rolling high or low.