Everyone is highly sensitive to slop, and it still looks like slop.

If you actually want something that looks decent, it feels like tool use would at least help cover the obvious blunders. Building layers to composite would go a long way to removing some slop here.

The windmill's axis shifts clearly and doesn't rotate at a uniform speed throughout the animation.

It's substantially worse than than an animated SVG of the same thing, and I don't think anyone can pretend otherwise.

Slight flicker on the door? The axle jumps to the right.

Right - the results seems to be inconsistent (it did a much better job with the eagle). Unsurprising IMHO given that you're essentially asking for a zero-shot of up to 16 coherent frames.