How did I not prove it? It's concrete numbers, really - if X amount of spirit allows you to cast one more Rejuv, and the same amount of Int raises your healing by Y%, then all there is to it, is compare the numbers - does the rejuv or the Y% amount of healing done increase give the bigger numbers boost? If Rejuv, then spirit is better, if Y%, then Int is better.
You can argue playstyle all you want, but this is as close as you get to actual "numbers" telling you if Spirit or Int is better. Remember, if your rejuv is overhealing, then you have to assume that your bigger heals from more int would overheal, too.