If one analyzes only the superficial aspects of the two religions, they are both mutually exclusive. The Creators want the elves to "be elves" which means separated from humans and their culture before they agree to return while the Maker wants the Chant to be spread to all the corners of the land before he agrees to return.
It's about being true to their heritage and culture; contact with humanity doesn't have anything to do with it.
Sebastian attempted to reconcile this by pointing out the similarities; that is, gods who won't return until their followers accomplished something; and claiming that perhaps they may be the same god and that the two religions are missing something about what he really wants.
Which blatantly ignores all the nuances details about the Creators, their view on magic, and the paths they can walk according to Andruil or Sylaise, two of their respective Creators: The Vir Tanadhal, The Way of Three Trees, and The Vir Atish'an, The Way of Peace.
Merril refused to accept this by clinging to the elven vision of the Creators and what they wish. She directly instigated division and conflict between the two religious groups; not in an harmful way, certainly, but she did by refusing to accept the possibility that they are the same god(division) and by clinging to the old dogmas that pit humans against elves since one groups wants to convert all while the other wishes to avoid this (conflict).
Not her finest moment.
I find it ludicrous that you think a religion is interchangeable with another because of a few similarities. It's a complex faith with it's own nuances, not a car that needs spare parts.
As for this, Merrill is right: the two faiths aren't interchangeable. Being elven and following the Creators simply isn't the same as following the Maker, and it's incredibly disingenuous of you to suggest otherwise.