"Full opposite rudder (not all aircraft require it and in some it may make things worse) without simultaneously relaxing the backpressure will only result in a spin developing in the opposite direction."
It's true what you say, but I haven't found a spin in the opposite direction a problem, because if you are proactive you ease off the rudder at the right time so that your rotation stops completely. I found that the technique worked well overall, but I certainly now prefer relaxing backpressure or maybe applying some slight forward pressure before rotation has stopped. As far as full opposite rudder is concerned, sorry, I was thinking of spin recovery in a particular aircraft type at the time. You're right, if you apply full opposite rudder for a small wingdrop you'd go back the other way.
"Not a valid argument at all."
That's hardly the case. When stalls are first being taught, it is easy to maintain control of the aircraft by keeping the aircraft in balance as it approaches the stall, and then if there is a wingdrop apply opposite rudder to stop rotation and then relax the backpressure to break the stall. I personally relax back pressure before rotation has stopped, but if you are more comfortable with stopping the rotation first then you may as well do it. Remember that there are a number of people, particularly inexperienced pilots, who get nervous with stalls, so sometimes keeping it simple can keep the stress down. I don't believe that having a firm stance again this technique will solve the problem. If it works, then this 'flawed technique' isn't really all that bad is it? I'm sure the CFI of GFS has a good reason for teaching this technique.