I agree that at the safety stop neutral buoyancy is the goal.. the amount of weight/buoyancy to achieve that of course depends on depth of stop and gear weight/buoyancy...but, if positive at safety stop air can be dumped to become neutral...disagree with 7lb estimate however; the weight of all the gear determines the needed buoyancy not just what the wet/dry suit generates at any depth...my SS plate adds -6.5lbs, adapter plate -1.5lbs, regs -2lbs and accessories around -2 lbs; notwithstanding the loss air weight or concurrent gain of buoyancy with some bottles....anyway, still of the mind that having too much buoyancy capacity in a wing/BCD is preferable to not having enough when needed....why guess or trim too close to maximum buoyancy you 'might' need at depth only to achieve the safety stop neutral state with wing/BCD empty or near empty? No big deal really, ESAs are not mythical feats of superhumans and safety stop depths can be adjusted to fit sea states and buoyancy if need be....still unsure why a suggestion to not be capable of positive buoyancy for the wing/bottle/regs/plate/trim weights/'extras' at the surface? One un-attentive moment after getting out of harness at the surface and gone is the gear to the bottom.Single-layer is a normal one-piece wetsuit. (I'd term your farmer John a 2-layer.) Since we should weight for neutral near the safety stop (or slightly above), the compression that matters to the wing would be about 7 lbs (based on the difference from 15 lbs, not 21 lb). Regardless, that's less than the 4 kg I originally ballparked above.
Lots of variables and always a matter of personal choice. Appreciate the dialogue and information.