[@mattmanganon] An overpowered character in RP's like this are also characters whose very existence forcefully alter established characters/lore in a way that contradictsthe core of them.

For instance, a normal human child, with a fairly rough life being given a weapon that is given specifically to those who inspire fear. No offense to any normal human who had a rough childhood, but teenagers don't exactly inspire fear. And given the previously given explanation as to how the kid got the ring, it would likely not have been yellow, as yellow is associated with inspiring fear not being fearless. 

Then there is the MAJOR personality change to a recognizable villain who has never (to my knowledge) shown pity in his quest for power. Killing (or trying to kill) people he had once called friend, even lover, if they threatened his chances. So to take pity upon some random kid who wasn't scared of him, especially to give that kid power, is as out of character for Sinestro as eating human flesh would be for Mickey Mouse. If nothing else Sinestro would be more inclined to simply vaporize the kid to eliminate another possible green lantern.

Of course the biggest hole I can see is in the previously mentioned explanation; Where it was heavily suggested that Sinestro met the "Gold Lantern" while wielding multiple spectrum rings and fghting the other lantern corps. So the whole ignorant of the others is a MASSIVE issue.