Tried a fair few types, Inc an old style barefoot. I've looked into many. If only I could afford a good newer one... Know many trail riders & endurance people who swear by treeless. Like treeless as a rule, tho barefoot not my favourite - tho as said, only tried old one.
With treeless generally - more or less depending on type - they may be little more than a glorified bareback pad, often don't distribute weight well, all the pressure is over the stirrups(when pressure on them) & girth. For that reason, it's often advised not to girth them up tightly - which can make the saddle less stable, esp on a more... rotund horse. That's why they say you need better balance. Modern treeless with more rigid panels, or broader pressure distribution have addressed that, to a larger degree. Many don't provide enough - sometimes any - spinal clearance, without using a special pad. Some have panels though, so special pad not needed. Many are not very adjustable - tho some have removable & changeable panels. And as you've mentioned, many have no/little 'twist' so they can be wide & uncomfortable for some, esp on a wide horse. I've found all I've tried to be like that, aside from the Freeform with the moulded seat. They may need a breastplate & crupper to keep them in place, esp going up or down hills. Some don't have 'D's to attach things like that, or not strong ones. So, when looking at different types, they're the main considerations imo for finding a good one.