With that in mind, my opinion is that the principle of least surprise should guide the coders. Current default should not be (or, have been) changed. That is to say, you should default to offensive when you initiate a new attack against a new victim, same as if you hadn't already been fighting someone else in the last 10 seconds.
If they hit you first, that's different.
This may be best to move to an ideas thread though, depending on what the staff says about this in relation to the recent changes.
If we had an effective 'switch target' command that might be different but as of right now we do not have one that is functioning the way that is described here, and on top of that, with postures taking time to change, it would allow someone (as the original post made plain) to game the system.