The only tangible advantage that the grenade launcher offers over hand thrown grenades is the three-round burst option. Which is pretty powerful, yes, but it'd be offset by having weaker individual grenades, the issue of spread (which could lead to wasted grenades or friendly-fire accidents), and the fact that you have to carry the launcher, which means choosing between a medikit or a secondary weapon.
Further, is stun
really that useful? Think about this seriously for a second; you need to take a grand total of 10 aliens alive. The exact species of those aliens doesn't really matter. Unlike X-COM Apocalypse,
there is no benefit to taking one of each species alive, and there's no ongoing benefit to live captures after the 10th. Research topics on each alien species are provided just as easily by a corpse as they are by a live alien. Once you've bagged your 10 live captures to open up
Live Alien,
The Alien Mind, and
Odd Behavior as research topics, stun is just another damage type. It's actually inferior to
killing them at that point because they can wake up from it.
And the game lets you use
lethal grenades in the launcher already. In three flavors, I might add;
Explosive,
Incendiary and
Plasma. I'm not seeing a prolonged balance issue, if there's any at all; you already have hand-thrown stun grenades and electrolasers, so taking live aliens isn't particularly hard (unless you insist on starting as soon as you get stun rods, which is silly IMO). What's wrong with making an easy task easier?
Another thing before I forget; it's another topic to research, too, meaning more time spent on less-than-lethal options.
Just like the plasma grenade, you'd need to research the hand thrown variant before you can develop a launcher delivered version. With the addition of Electrolasers in 2.3, you could comfortably skip researching alien gas entirely, both hand thrown and launched; it's much easier to just go
stun rod + D-F cartridge = electrolaser, since you actually need a
live alien, as well as autopsies of the 3
main alien races, before you can even start researching
anti-alien gas.
