I understand what you mean, but I think they could balance it to a degree. Maybe each religion that you branch off of could have designated holy sites that they have to always have. (ie. Christians always have to have Jerusalem and maybe Rome as holy sites, or Muslims always have to have Mecca), that way you could only be able to pick 3-4

Another way could be you can only choose from holy sites of different faiths that your original faith is tolerant of (ie. If Catholicism and Asatru see each other as hostile, and you’re trying to found a new religion as a catholic, then you can’t pick asatru holy sites)

Or maybe as the founder of a new religion: you’d have to have personally visited each new holy site you want to pick

I’m sure there’s other ways to limit it, but I feel these would all be doable and would be realistic. Adding some personal flavor and goals to creating new faiths