That seemed to be the case for GJ anyway. That he learned so quickly was attributed to QZ internal energy base. Plus the theories of QZ internal energy is related to the YJ based XL18P.
This doesn't invalidate SHL's effort. If he had poor instructions and internal energy that wasn't particularly compatible, the combination of the two leading to a fire deviation isn't farfetched at all.
Furthermore, GJ's 2 years of QZ training is superior to most other people's. Not only was he personally trained by Ma Yu (the best QZ master at the time in terms of internal energy), GJ's character was also very well suited to QZ meditation.