Excluders don't really help, some 'muzzles' use small mesh 6mm that the bees struggle with. The AH just pick them off as they squeeze through. I tried 10mm mesh and didn't work either, of all systems the 'lyre' type seems to mildly inconvenience the bees and generally inconvenience the AH.
AH only enter a weakened hive so restricting the entrance isn't the problem, they sit as close as 5cm (2") from the landing board and the bees stay put.
Ben, like most things they will weaken a strong hive and kill off a weak hive. Main problem is the bees not foraging so the idea is to move the AH back from the entrance, they don't like being trapped in a cage / muzzle. They can get through 7mm gaps so can walk past the muzzles no matter what people do so the 'sweet spot' is where the AH are put off and bees don't notice.
In time they will adapt but the idea that they ball the AH and cook them is true as they do it here, but it takes 20 mins and lots of energy to kill one AH. They only do it if they land and try to enter. Biggest problem is they appear mainly Sept/Oct so end of season so reduce foraging then. They say one or two are not so bad, at a distance, but three+ and they will cause problems. In time they will co-exist, as ever, as the AH do eat other things, just when they zero in on something they are very persistent.
Quick fix is just chicken wire, you can see the hornets in this video and the bees going round it. The wire is ok but the bees sometimes hesitate.
https://www.youtube.com/watch?v=PmRnYHiRnWw