Larian, and many of their fans, like being able to do weird and wonderful things in the game, regardless of how silly those things seem. As far as I can tell, the Larian view is that you should take responsibility for playing the game the way you want so that you enjoy it; which is fine for a game that is SP and co-op MP, since there is no competitive aspect or possibility of antisocial MP behaviour.
So from the point of view of the player finding exploits when part of the game goes into TB mode, there is no actual problem to solve. If you want to look for and use exploits, do so. If you don't think exploits are the right way to play the game, then don't use them.
Of course, if the AI is using exploits in the way the game works, then there is a valid criticism.
I don't have any particular problem with the way the game currently works, because I only play SP, and I don't spread my party out very much. When combat starts without all characters present, I choose to join the absentees in combat, or do not choose to join them; simple.
Even better ( from my viewpoint ) would be to have the game play in RT, but that is not the game we have.
