Saddles are generally used to help riders with stability and more importantly, distribute the rider’s weight over a larger surface than bareback provides, so avoiding sore backs.
When it comes to horse’s backs, when riding bareback as adults, not as lightweight kids, horses may get sore.
While there is a place to learn some skills riding bareback, having the horse’s back in mind demands we go light on bareback riding.
Bareback pads help with that, treeless saddles are a next step, then all kinds of saddles with trees.
When talking rider’s stability, stirrups are crucial to that and help keep the pads or saddles in the middle.
A tree also helps best for that also.
As you have read, along with cinches, breast collars and cruppers also help keep a saddle in place to some extent, but would not depend on them that much.
What you may heed as a warning, any saddle without a tree will tend to slip from side to side, so be very careful to be quick to kick the stirrups loose if you feel that happening, don’t want to cause a wreck.
I would say, stirrups added to any other than a fairly stable, properly cinched saddle with a tree is just not very safe.
In fact, there are plenty of saddles with trees that you can practically ride without cinching but snug, they won’t be easily turned.
Not so with treeless or bareback pads.
Saying all that, plenty of people like treeless saddles, including Cashel type ones, so why not try and see what you think, how it fits for your horses and your riding?
Several sellers will give you time to try one out, buy from them and you can return it if it is not what you think.
When it comes to saddles, each one of us likes what fits us, not necessarily what fits others.