You're really misunderstanding evolution. Metaphorically, mutation is like a faucet dripping a tiny drop of variance every generation into a bathtub full of a population's genetic variance; IOW the ratio of new variation to existing variation is not metaphorical, between 1/100000 and 1/1000000.
Without this reservoir of existing variation, removed by things like inbreeding, your population becomes extinct and mutations won't save it (this alone falsifies the notion that mutation is immediately driving evolution). You don't seem to know that. You seem to think that evolution doesn't happen without new mutation.
Given that ratio, if God stopped all new mutations tomorrow, evolution wouldn't slow down perceptibly for a very long time.
Decades are a very short time. I think you'll find that if you extrapolate decades out to evolutionary time scales, the numbers work out. Have you tried that?
None must arise simultaneously. You've got major misunderstandings of evolution, population genetics, and developmental biology.
Why? What's going to happen to him?
I think you've set up a movable goalpost with the deliberately vague term "structure" that you'll move as people provide examples of how evolution (not mere mutation) creates new structures.