You think a lot of the same things as Descartes, and as far as many of his theological points of view, he's in a tiny minority.God's nature is to be all-powerfull, therefore he "decides" based upon his nature, because God cannot change. (not changing is in this case not a limitation to power either) If Gods nature is to be all-powerfull and he "decides" based upon that nature, then He "decides" the more powerfull route because he must in order to be all-powerfull. The more powerfull route is not to break promises, not to sin, or not to not exist. Rather than breaking promises, sinning, or not existing.
...you do not have the power to not exist. It's a little late for that, don't you think?
You can't just say, "this is not a limitation of power", you have to explain why it isn't.