AIO is best used as a paint cleaner. It should be the step after polishing and prior to using a sealant, wax or glaze. Some people say that it has protective qualities, but I have never seen that. I still say it looks best as a paint cleaner and that's about it. I don't know anybody that just slaps AIO on all by itself anyway.
If you use AIO over #81 then it is going to remove any thing that #81 left behind. So any fillers or oils that are on the surface will be cleaned off. Since #81 is mostly oils and fillers anyway, I don't think there would be much point in following it up with AIO.
If AIO does have any protective qualities in it, then I can almost guarantee you that they are stronger than #16. Any synthetic is going to be more durable than a carnauba. I still wouldn't use AIO for protection, but I guess it doesn't hurt. The next step after AIO should be to put down a sealant with some real protection qualities to it. Something like UPP, SG, WG, or even NXT and #20 would be good choices. Any sealant would work great and be more durable than #16.