I apologize if I was reading too much into your comment about "GM vs. Players." And, as I've said, what works for you is gravy. However, in my experience, and in the experience of the vast majority of gamers I've talked to, ultimate power is boring. Stories thrive on conflict, after all, and an "I win" button is not conducive to that.
You can make the argument that the PCs are not the only ones who can press the I Win button, but then all you've done is make someone else the winner in a game that shouldn't have one. I'm a long time fan of Exalted (if you're not familiar with it, the gist is that every character is a demigod originally incarnated to kill immortal chthonic entities from before time began), so trust me when I say I have experience trying to balance powerful PCs versus powerful opposition. It's
hard.
Furthermore, while one of the PCs is busy binding Mab to be the waitress at his favorite bar, what do you do with the PCs who
didn't make a character capable of breaking the game over their knee? Give the ritualist two or three opportunities to do his thing at most, and he'll be more powerful than the entire party combined, which tends to cause no end of ill-will between players. The spotlight should go on everyone equally, and it should definitely not highlight people who prioritize mechanical strength over those who just want to tell a story (which, as mentioned above, revolves around a valid conflict).
Just to be clear though, I'm not trying to stop you from giving this concept a whirl if you really want. This post is, if you'll forgive my pretensions, sort of a Public Service Announcement about ideas for GMing that are
usually bad for
most groups. I have no interest in forcing people to subscribe to my views, but I have been GMing for years, and if I'd been able to give my earlier self this advice, it would have helped a lot. Take from this precisely as much as is helpful for you to have fun. As the Chaucer has written*, "take the wheat, and let the chaff be still."
*Technically, he wrote "taketh the fruyt, and lat the chaf be stille." But I wasn't sure how many people on the forums knew Middle English.