You are correct, twinking is not an exploit, and no one has said it is.
The exploit comes with indefinite twinking, which is done/caused by leaving a warzone before the end, to avoid the rewards. While this is hard for a player to prove 100%, I believe the OP mentioned things like "Observing several 49's leaving just before the end, repeatedly."
So as you say, twinks are not an exploit, nor is the concept of twinking being discussed here.
As "benefits" are subjective, one could make an argument that these Infinite Twinks (the act of remaining a twink indefinitely)are benefiting in personal reasons (ie. E-peen, Roflstomping, etc...), and that the act of -not- getting conventional rewards allows them to continue receiving their own personal benefits. If their personal benfits are disruptive to others, and are not part of natural gameplay, then it's a problem.
TL-DR: Twinks aren't exploits, Staying a Twink indefinitely is. That's what's being argued and you are arguing using missunderstood terms/concepts.
staying a twink indefinitely is not an exploit. if someone wants to leave a warzone every time so they dont level up to 50, where PvP actually has some semblance of meaning, thats their own choice. maybe they werent hugged enough as a child and enjoy trolling people in video games, it doesnt matter why they do it.
you get XP regardless of winning or losing. eventually, by finishing warzones you will leave the sub-50 bracket, and never have to see those evil infinite twinkers again. if you cant handle bullies on the interwebz, i dont know what to tell you. it is not bioware's job to make sure nobody ever hurts your feelings by repeatedly beating you in a warzone.
if youre whining this much about a gear imbalance in the sub-50 bracket, i cant imagine what your opinion of 50 pvp is.
enough of the whining. either finish grinding your wzs to get to 50, or level a different way. its not like the wzs are too complicated to figure out after a couple of warzones in the 50 brackter