I assume it's because it comes from /tg/, and /tg/ didn't have to account for instakills as you can't get roundstart prosthetics and you can't choose any synthetic species. (at roundstart anyways, and they don't die of EMP when I played around with them on Local.) And actually we did make a PR to remove EMPs from them but it got closed because fox said "I'd recommend implementing TG's latest round of balancing for revenants and we see how that plays out before we consider just removing this ability." We haven't done that yet. For fuck's sake. The last PR made that even TOUCHED revenants only added them to game preferences. That was done exactly ONE month ago, and not anything has been done to balance revenants.
their literal only instakill spell to my knowledge is EMP, give them more instakill spells that effect everyone instead of a small group if you're really wanting to keep that for fuck's sake. If you won't even bother trying to port the balances or work on making the spell less murderkill for those people, then either give them another killing tool and make them what they never were meant to be (a ghostly killing machine) or remove it and turn it back into what it should be, a minor annoyance that sticks around just to pester the crew.
Lings have EMP because they're supposed to be murderers. They're supposed to fuck the situation of the station, they are not just an annoyance.