I prefer the simplicity, but I see the point.
In example you have 6 units that should lose to a superior force. In the first round the attacker has terrible rolls and only lands 2 hits. You have 4 units remaining, but to save 2 units you have to leave 2 units behind for the attacker to roll against. In effect it becomes low luck by taking x amount of units off the board but you get to preserve the remaining 2 units.
I think its a better balance for the defender allowing low luck scenarios to occur, but requires the attacker to first experience an ill-fated roll. The trade-off is that the defender doesn’t lose all their units in the process, which is the biggest gripe from low luck as I see it. It gives the attacker the territory they wanted, at the expense of a few units escaping.
I would posit that the lone exception to my rule would be TT cannot retreat unless they are escorted by surface warships.