As a heavy weight rider who rides treeless, and has for years, she leaves a lot of speculation in that "study".
First of all, what kind of treeless. What kind of pad? If you ride a treeless saddle, you should understand that the padding under the saddle is super important.
I ride in a Freeform with a Haf pad underneath it. My horse has never had another saddle on his back, this is what he was started in. He's a 14.2, long backed, half arab with a heavy weight rider (I'm over 200#'s) who is destined for endurance, so we have put a lot of miles at speed in this saddle. He has NEVER had a sore back. His chiro and his vet compliment him every time they see him.
I would not ride him in a treeless without a quality, pressure spreading pad under that saddle.
Therefore, I want to see a study done with various treeless saddles (not all are created equal by any means) with proper padding under them. Then compare it to the treed saddles. Until then, you really can't make anything out of that article.