Lots of Top Gun pilots here!
But it is a good question, because there is more to it than it meets the eye.
First, you can make hundreds of landings and the sluggish A-330 A/THR will lag many times, without going below VLS, but well below VAPP. Below VLS is indeed a rare event (seen it twice in 4 years)
Second: GS MINI is fantastic, except if you are in the A-330 with its sluggish A/THR. When you see you are 6 kt below VAPP and increasing and thrust doesn't move a freaking decimal of N1% even after several seconds, you have at least the right to name it sluggish.
Third: If you are flying the A-330 on behalf of an airline full of OM stabilized approach restrictions and FOQA, this scenario is way different than if you are in a more relaxed, pilot friendly or pirate airline. In the former, you can be sacked or demoted for an unstable approach, so if you have this situation at 500 or below, you should go around. Or shouldn't you? How many knots below VLS should trigger the go around decision? Depending on the trend? What is my ops department opinion regarding that matter?
There are deviation call outs. The question is What do you do when the PM says "speed" and A/THR is engaged?
a) disconnect the A/THR and carry on manually
b) do the thrust levers momentarily above CLB detent technique
c) say "correcting" and hope that the A/THR decides to correct and start increasing N1, at least enough for the trend to be on the recovery side, we will be good soon before flare, lets see...
d) go around because you are not stabilized anymore.
You might very well decide a), b) or c) and then be sacked. Even Maverick could be sacked for that (and Gus sent to CRM rehab. "I got your tail, man").
You might choose d) and then be questioned about an unnecessary go around "come on, man, it was 2 knots and already with positive trend, be a man". Some good airlines will not question a go around, but others will.
So the question that the original poster made is a very good one, indeed.