In the first couple of decades of the 20th Century the U.S., British, and Australian Armies experimented with “flexible tree” saddles. There were the 1912 Experimental saddles in the U.S. and the 1912 Brit/Aussie UP models. Within a very short time the U.S. and British had given up the idea as it just didn’t work. There were attempts to modify the original design but they were not effective in bearing weight and caused an epidemic of sore backs. The Aussies went a bit longer, but then realized it wasn’t working for them, either. The idea was gone before the start of WWI.
Not only did they sore up the horses they were not very “robust” and did not hold up well under field conditions. While this might be of less importance to a civilian user who will not be pushing equipment to its limits it is a warning.
The military load in those days ranged from about 250 pounds in U.S. service to 290 pounds in British and some Continental armies (The Austrians were actually a bit north of 300 pounds). Most modern civilian riders are below this unless you’re talking about people who seriously “horse camp” or hunt game in a wilderness milieu on a Western saddle.
I get the difficulties of saddle fit. And I understand the motivations to look at things like “flexible trees” or “treeless” saddles. IMO they don’t work over the long haul because NONE of them effectively distribute weight. If they don’t do that then they don’t fulfill their primary duty, which is to protect the horse’s back by preventing areas of weight concentration. Mind you, a badly fitting treed saddle fails in this, too. But I don’t know of many who recommend badly fitting, treed saddles.
With saddle fitting you’ll have to kiss a lot of frogs before you find your prince. WAY too many people are unwilling to buy good quality saddles 'cause they are trying to “economize.” But with a good saddle you not only get a good quality of leather, workmanship, fittings, etc. you also get some GOOD ENGINEERING!!! The wise horseman/woman bites the bullet and buys good stuff for their horse. It means fewer vet bills, fewer months in training with somebody who has to try and fix problems caused by poor choices, makes riding more pleasant and productive, etc.
In short, quality doesn’t cost; it pays.
G.