Hmm. In that case, my opening bid would be to explore a domain for clerics what have been ditched by their gods and adapted to the problem – I tried something parallel to that with a Renegade wizard tradition, here: http://harbinger-of-doom.blogspot.com/2016/01/d-5e-apostate-and-renegade-wizards.html.

Obviously, if you want to build it out of the mystic, more power to ya. Oh, and Cam Banks is on the record as agreeing with you, so I think that makes me wrong from first principles. 😉

Nothing arcane about the Dragonlance mystic. Think of it as a divine sorcerer, with a single domain (in 3.5 terms). The favored soul is probably the closest to the concept. The cleric may work as well, though we Dragonlance fans would like the Dragonlance mystic to be a distinctive class from the cleric.

Thematically, the 5e mystic has some concepts in common with the SAGA mystic’s spheres.

You could fake it if you really wanted, but I would say that the 5e mystic isn’t trying to be anything like the DL mystic. For the DL mystic, I’d look at the Theurge wizard or favored soul, since I think you want a healthy arcane/divine blend?

I was really surprised to see the wu jen as a subclass.

It’s massive ain’t it? I believe we could wait though, most times it’s worth it. 😉