everyone has different opinions on how to do things with their dogs, if your system works with what you have got and turns out consistently good workers , stick to it, but never decry another mans system just because you use a different one, it may work just as well for him as yours does for you.
I HAVE seen good young dogs spoilt by premature entering,terriers and lurchers, i have not seen dogs spoilt by entering a bit later ......yet.
Sometimes we, as handlers, borne from years of hands on experience, know whats better for the longevity of that dogs working carreer, and how to go about