What is the 'right purification steps' ? If one is subjectively happy with the product, and if the potency isnt reduced (if one can breakthrough with 50mg or less), then does it really matter to 'purify' it?
BTW, I dont think an A/B will have better yields, in fact I would say it will be smaller yield because all the steps at the end will be limited by the first step. There have been tests done before on supposedly 'spent' bark from an A/B where there where still alkaloids to be retrieved in the bark. I think A/B was very necessary when defat was still something people did, but since defat is a prehistoric method and very wasteful, personally I dont see much need for A/B (Except for the cleanliness when working of course, its def cleaner to work with a liquid when mixing the solvent than with a sludge. Also if one uses a separatory funnel, which is impossible to use in an STB).
Regarding advantages and disadvantages of A/B and STB and others, the FAQ overview on extraction is an attempt to sum that up.
As for yields, yeah it depends but I would say most yields, regardless of tek, will fall between the 0.5-1.5% range. If you're significantly under 1%, try to improve your technique (for example making more pulls and/or more acid boils if its an A/B) and/or getter bark . If its 1% or more, no need to compare, just be happy