I don't have experience with Audeze planars, and I wasn't comparing planar to planar. There are some planars that clearly don't have very low distortion in the lowest octaves, such as the Ananda. Sundara doesn't have the lowest distortion, either, if you look at the measurements of many planars. Audeze's offerings are quite good in this aspect as well. When it comes to dynamic drivers, however, they always do poorly in comparison. My ATH AD1000x has a massive 54mm driver. It should be able to push a lot of air, and Tyll's measurement shows that it has pretty low distortion below 40hz, relative to 98% of other dynamic headphones. Compared to the Sundara, however, the AD1000x is not even close, and that is audibly so. To get a dynamic driver to rumble as hard as a planar, I think you would have to take desktop speakers and seal them around your ears. lol
To get planars whose efficiency are rated between 89-94dB to audibly distort, you would have to pull a lot of power, which is probably why this aspect of these planars don't get mentioned much. People also don't do bass boost EQ much, because this would easily require their (already beefy) amp's output capacity to quadruple easily. I've tested that my Sundara can pull up to 9W from my Crown XLS 1502. Nine. Freaking. Watts! These are transient subbass slams, and of course you can only safely do this with a few tracks and movie scenes if you like to keep your hearing. It's very, very fun. These kinds of rumbles and thick slams would damage 99% of dynamic drivers.