This is not strictly correct.
While it IS true that electrostatic headphones in general have somewhat limited excursion when compared to dynamic headphones, this really only impacts the maximum SPL of the lowest bass notes, where a fair amount of air needs to be "pushed." So, compared to good quality dynamic phones, Stax tend to have a little less bass "impact" or "punch" which is related to large excursions. Don't confuse this with bass "speed" or ability to reproduce low bass- Stax phones excel in both these areas. It's just that there are limits to how loud an electrostatic can play at 30 Hz. Bass "impact" seems to come from short, loud low frequency bursts, and this requires generally more excursion than electrostats are capable of.
I think that Stax headphones ARE less fatiguing than many of the dynamic and planar designs- for example the Sennheiser HD800 and HiFiMan HE-6, but I think this is because the Sennhesiser HD-800 and to a lesser degree the HE-6 achieve their high levels of "detail" by having big peaks in their treble response. Loud treble can be very fatiguing. It sounds kind of great, but if you listen loud, your ears will hurt.
Stax headphones have some treble peakiness but it is gentler, and in general the Stax have a more neutral, less aggressive character, with very good midrange- I find that when I adjust the level to a nice loud volume that I prefer, I am setting it based on what I hear in mids and upper bass, and if the treble is a lot stronger than these mids, it will make my ears hurt. And probably eventually damage my hearing, I might add. But I find that that my while Lambda Signatures have some treble emphasis, it is nowhere near as much as the HD800's. I can listen quite a long time to the Stax, although with Stax I have other problems- the leather earpads make my ears hot, which doesn't happen with velour earpads like the HD800s have (or Beyers, for that matter.)
So I would say that Stax headphones ARE generally less fatiguing, but it is related to flatter frequency response, and not "air pushing" ability.
I suppose it is also true that excursion limits of the electrostatic transducers DO limit also ultimate maximum midrange and treble SPL's, but really Stax (and other electrostatics) can produce WAY HIGHER SPL's in the mids' and highs than ANYONE would listen to, so this never becomes an issue.