Ultima wants to use Clive as a vessel, a final Mythos to complete its design and remake the world in a form that excludes humanity. The game's final act is built on Clive refusing this not through superior power but through the completeness of his will. Destiny carves its own path because he keeps insisting on carving it, even when the force trying to redirect him is effectively divine.

The path requires losing things. Dion's sacrifice, Joshua's condition, the cost of every Crystal that has been broken — it accumulates into a world that is genuinely different from the one Clive started in, at a price that the ending does not pretend was cheap.