Strongly agree with OP.

About half way through my first play through of existing content, I began separating (unlinking) my stealthiest or most charismatic character and had them do most of the exploration solo, simply because I did not like how the game automatically decided where the other party characters would move/arrange themselves.

In my opinion, Pathfinder: Kingmaker has the best character placement/control system I've played. It is easy to customize where characters should form, and the AI was apt enough to make adjustments to the form when a spacial limitation exists. Furthermore, the PF:KM system was much more lenient in character spacial geography - the buffer between characters/objects is much more fluid, allowing for better movement in confined spaces. Currently in BGIII I find myself using the jump/disengage bonus action far too often for simple movements between avatars that seem obviously accessible (unsure why disengage is a bonus action for all classes to begin with, but that's a separate issue).