The way I see it, if you look at all the facts and contradictions, there are two main possibilities:

1) This is another Un'Goro or Sholazar--another test, another experiment. The Titans are pure Order the same way the Old Gods are pure Chaos--they don't care about our well-being. It explains why they gave Azeroth an important artefact like the Well of Eternity and then disappeared.

2) Deathwing was not meant to be. It's possible that Aman'Thul, despite being able to see the future, couldn't see what would happen if Neltharion wasn't just taken out of the equation, but turned against his allies. In which case, it's lucky we have World-Shaman to conveniently become essential.

On the other hand, at least we finally have an answer to the question of "Just how does time travel work in Warcraft?", considering the question of "What happens if we remove the Dragon Soul from the past?" is answered with a handwave of "we'll stop time lol" instead of "it's an alternate timeline, it won't screw with ours directly."

God only knows where the splinter realities and predestination fit in, though.