Having read through 6 pages on this topic, and seeing it to be essentially an "Aussie" issue, in this forum at any rate, I hesitate to venture an opinion - but what the hell !! I am a "longish term" 25 year Airline Pilot, from a GA background, and I maintain GA interests (own plane etc). I am also in Airline Check and Training.
My two cents worth is that background/experience does not matter, and that "command time" is a meaningless measure to apply to an entry level pilot to an airline (and by "airline" I mean ops in multi-crew 10 + seat aircraft).
So long as the entrant holds - the basic requirements for the job: receives thorough and adequate initial training as part of an organised training program ; and has THE RIGHT ATTITUDE - then the skills appropriate to progression to command (NOTE - skills, not hours) will be acquired, and this can be done over a relatively short period of time - hard to put a number on this, but my subjective judgement would be 2 - 3 years. The reason it takes longer in GA (anywhere) is in part because in GA no organised development/targeted skills training takes place - it all happens by a sort of osmosis, whereas in GA in the main skills considered herein to be inherent in time on type/in a type of operation are acquired largely by "trial and error" - in fact you can extract the core elements of all those "scares" the "heroes" have had and teach people how to avoid them, rather than have each successive generation repeat the mistakes of those who wnet before - but enough from me.