Dude... its all make believe, so you've no idea what is the same as what. All you can speak to is how you see it in your own subjective imagination. In your imagination the other make believe energy melee weapons are not the same as the make believe lightsabers. But none of it is real so there isn't any basis to insist on differentiating the two... other than your subjective disdain for Finn and consequent need to find things to criticize about the character.
And so much about Star Wars is utter bullocks from a real-life/physics perspective that I am always fascinated to see folks nit-pick particular hills to die on... as if this one non-"realistic" aspect of the freaking fairy tale completely ruins anything... like the fact that the ships make noise in space and fly through space like airplanes flying through air is A-OK... but the difference in "training" needed to wield one imaginary weapon versus another imaginary weapon... well that's just a bridge too far... Yeah, nah, I'm not buying it. More likely... like I've said, that you just didn't enjoy/connect to the character and a lot of these, non-sequitur, contradictory, inconsistent "reasons" are post facto justifications... because as I've already demonstrated, you really weren't paying much attention to Finn's character in the first place... so to try to blame it on the supposed "weigh ratios" between one make believe prop and another make believe prop just doesn't add up.
Let me ask you this... were you bothered at all by the way Thor flicks Mjolnir up in the air, end-over-end and catches it like its a pencil in one scene, but then swings it with leverage like its a baseball bat in another? Did you ever even think about it? I'm guessing most folks didn't... because when you like a character and enjoy the movie, you don't get bogged down with such trivialities. Its only when you don't enjoy, that you start nit-picking every little trifle, to intellectualize your largely emotional dislike.