On the whole 'big breeder' note.... some powerfeed as well. Just because they do it doesn't make it right.
It is more prudent to do what is best for the animal. Once in our care it is our responsibility to keep them in the best health. Feeding f/t is the best way to do that. I don't want my snakes bitten or parasite ridden. Plus the fact that we keep far too many reptiles to be having live rodents here (they STINK!!)
Before calling the kettle black.... be sure you aren't the pot first. Converting a Royal may take longer than three weeks, it may take less time. It all depends on the particular Royal, not all are the same. Don't go calling names, he is only looking at the best interest for the animal. I have quite a bit of experience, maybe not on the level of a 'big breeder', but enough to say that he is right.
Just keep walking and ignore the monkeys...