A good title to help further his career seems like a valid concern (even if the title itself may not be legitimate), but so are your concerns.
You could put the burden of finding a solution on him? Share your concerns - that you did the bulk of back-end technical work, and feel that giving someone else the CTO title would devalue it. If he can find a way to get a better title (CTO or something else) without devaluing other roles, then you would not object. Since he's the one that wants to change things, it seems fair that he come up with a solution.
You could put the burden of finding a solution on him? Share your concerns - that you did the bulk of back-end technical work, and feel that giving someone else the CTO title would devalue it. If he can find a way to get a better title (CTO or something else) without devaluing other roles, then you would not object. Since he's the one that wants to change things, it seems fair that he come up with a solution.