Using you argument that as long as the shooter is "up to snuff" the gauge doesn't matter, let me ask you why so many advocate extended magazine capacities for HD abd why some also wear a side saddle? Why not just rely on the good old single shot if one is conficent they will shoot with perfect precision under exigent circumstances? It is because the best shooter can be off the mark.
Next question. What poses the greater risk of collateral damage from , assuming the same velocity; 5 pieces of OOO from a .410 or double their equvalent weight in #4 Buck out of a 12 gauge?
Laslty, given the same loads as above, which is more likely to put an instant stop the threat if your hit is 8" to left or right of center at a distance of 10 yards?
it is well and good to train to be dead on accurate and to strive to put every piece of shot on target, but chit happens under extreme pressure. Plan for it. Ig a .410 is best for you, go for it. All I am saying is that it generally is not the best HD shotgun for the average person.