So, is this a matter of trust, or control? It seems to be a control issue to me. You want to have veto power over anything outside the PHB. Your "problem player" probably sees it the same way and doesn't like having someone have control of his character.
Your phrase "...Reserved the Right to Remove It" again sounds like a control issue. You need to get past that or you and this player are probably never going to correct this.
Why not instead say, "Looks good. I'm a little concerned about this ability, but lets give it a try. If I think it is causing problems we can discuss it." Any subsequent discussion should include why you think it is a problem, not just what to do about it. Perhaps rather than removing the ability, someone may be able to suggest another way to correct the problems you experience because of it.
My opinion is that, when it comes to players creating the characters they will play, you need to make things more of a collaboration instead of a "it is OK unless I say no" attitude. It may be your world, but it is everyone's game. Everyone needs to have some control over their particular parts.