at least a sword of me3 is more plausible than the Project Larzues of ME2 fame. Also it would be safe to assume that metal working would have improved by ME3 period to slash and pierce most armors.
I guess you're right about the first statement, heh.
For the rest, you're basically describing a lightsaber of sorts. Metal is metal, you can't use a sword to cut through armor like butter, it doesn't work like that. And I haven't seen anything on the phantoms/Leng swords that makes me think they're anything but normal swords (without some sort of energy field around or anything).
By that logic we basically have swords that can cut through Tanks and APCs, heck even starships. Again, directing ME franchise into the bag with the other dozens of shooters/etc out there.
I'm just saying. N7 slayer was fun to play as. Phantoms got noting on em. I think the swords are made out of something like adamantium. Some super strong and sharp metal.
I wont disagree that the slayer was fun. But they introduced so much nonsense into the game that they contradict themselves. Like they've stated that teleporting was not a thing in ME universe by the time the trilogy takes place and yet what the Slayer, the Cabal, and the Kasumi like girl (can't recall the name) do? teleport as a dodging maneuver. That's BS.
At this point I'm doubting if the multiplayer part was truly considered canon on the franchise.
Yeah the phantom sword is a "monomolecular" sword, a fancy name that really doesn't say anything. For me is still a metal sword with a magic ability to cut through other metals.
I'm not saying some of these mechanics are not fun, I just don't want to see ME turn into that type of game. As I've said, it used to be a game placed on a hypothetical future not so different of what mankind could achieve at some point in real life. And there's a reason why we stopped using swords, bows and the like in modern combat.