Yeah, Execute is just overdoing it. Though he probably just wanted to see how big he can get in damage. The thing is, you can get 2 shots/turn with plasma pistol, as much as with sniper rifle (albeit with lower range and accuracy on second shot, though with no move and close range penalties either). And with proper crit build, you can get very decent damage per turn. On small targets you can use laser pistol. Also, they have an advantage of dealing a damage that is less resistant compared to mechanical and you don't need to keep a supply of W2C to deal with enemies like bots, bladelings and others like that.
Overall i think energy pistols are better than regular pistols, they may be one-trick pony, but they at least have this trick and this trick is decent. They still not that great, and need a buff, so they can be used outside of very specific build.