I know nothing of the WBM method so can't comment over points 1-5 but it seems to me that there may be substance in your concern over point 6. I have always understood that about 8-10 inversion in the first 30 secs( I prefer 8 inversions) were about right and about 2-3 inversions( I prefer 2 only) in 5 secs every thirty secs

5 inversions in 6 secs is better than a cocktail waiter can do

I'd certainly slow down and reduce both sets of inversions. I have no idea by how much the contrast will be reduced but it should help. I'd imagine that at 6 in 5 secs every thirty secs the Xtol must get quite bubbly. Mine did even at 3 inversions over 5 sec so I took it more gently.