User blog comment:USARMP/Ninjas in Mass Effect/@comment-3325589-20120408223908/@comment-1388547-20120410035744

Guns in Mass Effect mostly shoot much smaller rounds than present-day weapons, with much higher velocities. (Though there are a lot of oddball projectiles in the game these days -- regular slugs wrapped in "phasic envelopes," mini-flechettes, spikes, various exploding munitions, high-energy particle beams, streams of ferrofluid...) I don't really know how effectively those would wound enemies or penetrate armor -- or what kind of armor would be good for stopping them. It's entirely possible that armor that's good against ME 'verse bullets is weak versus edged melee weapons. After all, present-day anti-ballistic armor isn't always the greatest against low-speed piercing or cutting attacks, and some technologies I've heard about would allow lighter armor that's better against bullets but worse against other weapons.

In any case, I take the Phantoms and their swords as an acceptable break from realism for the sake of looking cool. It's a game, after all! And I usually don't have too much trouble with them -- just keep a sharp eye out, and make them high-priority targets when you see them. They're not all that tough, especially if your squad is oriented toward damage output.