It's not the same question, and that's the point of this article. Gravity acts equally on all your particles, so it doesn't cause any disruption (other than that gradient.) Magnetism affects different particles differently, particularly moving ones, as in electrons. The article says how a strong field compresses and deforms electron orbitals, to the point where covalent bonds fail. Field strength alone causes that, not gradient.

I don't know if we could measure the difference, but since gravity's force decreases with distance, I bet there is a difference between the gravity on the top of your head vs the bottom of your feet.

It's probably small enough to be negligible, but it should be there.

Are you so sure that you wouldn't be harmed in an extraordinarily strong gravitational "field", with field lines parallel to your body?

I imagine that the difference in force exerted on your feet vs. your head is significant, in raw Newton's rather than as a percentage. The r^2 is basically constant across the length of your body, compared to M, but it's not actually constant, and when M is so large, I imagine even small changes in r^2 lead to (relative to our scale) large changes in F. Is my intuition wrong?

You are saying the same exact thing as the comment you replied to. Differences in the force at the feet and head is exactly the gradient of the field. If you have no gradient the forces are equal everywhere.

You're describing a way for a meaningful gradient to exist, so it amounts to the same thing.

So, would a very strong gravitational wave wipe out humanity?

Certainly, but making one that strong is essentially impossible even if you have a convenient pair of black holes.