The operative word here is "developed". I did not invent the idea; quite honestly,I don't remember who did. But I did develop it.
A game developer (or in this case, a rules developer) is kind of like a midwife. We take someone else's ideas and twist them into a more coherent and playable format as we help them to be born. Sometmes it just involves tinkering with the rules a little on somehing that already works. (A good example of that would be the 2nd edition of Naval War that I developed for AH as a labor of love. It started as a goofy article I wrote that was just a compendium of "house rules" that my gaming group had come up with in my basement, and ended up as a whole series of optional rules in a subsequent printing/edition.)
I hammered and twisted those psionic rules forever, and inflicted play-testing on the gang until they got sick of them.
Yes, I probably lobbied for their inclusion in AD&D. No, Gary did not love them as I did. But he was wise enough to kow that for D&D to continue the phenomenal growth, we had to offer stuff that others might like even if one or more of us didn't.
5 or 6 of the greatest days I spent at TSR are when Gary and I literally locked ourselves in his office each day from 9 to 5, had all calls held, and proceded to cover the walls and floor with cut up rules booklets and legal pages as we decided what would be Basic and what would become Advanced. It was the first time that the game and all of the supplements,additions, add-ons, magazine articles, etc. were assembled, analyzed and dissected. We had some great friendly arguments...