Treeless saddles need to be fitted, just like a treed saddle. They also need correct padding to make sure there's spinal clearance. Not all horses go well with treeless. Weight dispersion is something you address with fit and padding.
For what it's worth, I ride exclusively treeless. My horse has never bad any kind of back issues or girthyness since switching. Last time I tried a treed saddle on him (with the help of a fitter), well...it wasnt pretty! Let's just say that my horse said NO very loudly.
Anyone looking for more info on treeless is welcome to PM me for info on a group that is exclusively treeless. They can help get you going.
Posted via Mobile Device