If League and AFL didn't exist the All Blacks would have zero chance against the Wallabies. NZ are so good in Union because it's either a minor sport for other countries (Aus, France, Argentina, Japan, England, etc) or over the top elitist with horrible pathways into the professional sphere (South Africa, which also suffers from the ridiculously hypocritical quota system).
Nobody in Australia wants to watch teams scrum for five minutes straight or not have the ball in play for 40 minutes of an 80 minute game. I went to Churchie and played Union there, and I can tell you that very few people I went to school with passionately support Union as a code anymore. If support is waning from that demographic then the code is officially on life support in Australia.
Can you imagine Inglis in his prime running at blokes like Beale and Phipps? Barrett would get targeted big time in defence in League, like he'd be in a different world of pressure in defence that would hurt his attacking output.
You can hide in Union, there's nowhere to hide in League.