there is a difference between nonsense unrealistic for a plot reason and some sci fi explanation. They could have with some creativity made a proper explanation without defeating basic physics entirely taking the sci out of the sci fi.
Honestly, I like your ammo idea and think syth'd ammo and engineering could have crossed over much better than the RNG "you're stuck with this" system we have (and whatever you want to call it for energy weapons, whatever it is that makes it go boom, doesn't have to change the ammo less gameplay).
People are just terrified of the game being ANYTHING like Eve Online though, even in areas where Eve does things pretty cool.