Star Trek actually had a plasma TORPEDO, though they did not call it that at the time: The Romulan weapon in "Balance of Terror." It was an absurdly powerful weapon almost on par with the Death Star; you may recall it severely damaged a star base buried many miles below the surface of an asteroid—and a second blast ATOMIZED THE ASTEROID!

Star Fleet Battles and Cosmic Balance both later defined it with technical specs; I never played the former, but played the latter a lot. I remember the plasma torp well: Unlike phasers, it lasted for three turns after it was fired, tracked targets and badly wrecked their shields; it also had a nasty habit of wrecking whoever fired it if they 1) made the mistake of firing it in the direction they were traveling at high (or even moderate) speed or 2) passed between it and the target before it dissipated.

Plasma is not your friend: It is a clumsy erratic weapon therefore nearly as dangerous to the wielder as to the target. Exhibit B is the only plasma we actually DO use as a weapon: The fusion bomb (though the fission-fusion version is not nearly as dangerous as, if less powerful than, the fission-fusion-fission variety.)

Lasers, however, can be precisely targeted to avoid all surrounding objects, and deliver virtually all firepower undiminished by range except at significant distances. They are more akin to rail guns in that respect: As long as nothing gets in the way, anything you point them at will be almost instantly annihilated (if something DOES get in the way it will be annihilated instead, but that is only possible for a split second between the time you fire and the time your target is destroyed.) Calling these lasers "lightsabers" is a bit over the top (and ignores their behavior,) but in the sense that they are "more elegant" (i.e. precisely targeted,) the comparison is valid.