If you define your natural weapon in a way that restricts its parrying capabilities, you are self-compelling.
No, you aren't. Fists by nature is not allowed to defend against weapons. IF you can provide justification (like “My skin is bulletproof, so I should be able to block a sword if I do it right”) then you can defend against weapons. A natural weapon is not justification in and of itself, since there are many things which one could define as a natural weapon. Fire breath being a good example of a weapon that you would have a hard time justifying it's use as a defense against weapons.
Anyway my point is that if you could normally do something, and are prevented by an aspect, that's a compel. If you normally can't do something but one person's flavor text allows them to skirt the rules, that's an issue.
Really? I'm not aware of any.
Yeah I went and actually checked them out... There are issues, but they are minor. Human form takes a supplemental action to get rid of, and human guise may fall away at inappropriate times. So you're right on that one.
Nope!
If your obvious weaponry causes you problems, it's a compel. If it causes you no problems, then it's nothing. And compels aren't bad, as we can see from the fact that aspects are generally two-sided.
Yeah, I'm willing to concede that point.