Mine also - I class them as semi-pros - i.e. pros for part of the year.
Playing for an ARC is not going to keep them in the country for long, but it could give them confidence that they can stake a claim to a Super gig on the back of it. At the same time they would know that it would give overseas scouts a decent look at them.
So it could keep them in the country for a little while.
The other side of it is that playing in an ARC would give Super coaches a higher level of rugby to assess future recruits in.
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A hypothetical ARC would have to be primarily about exposure and development of players, coaches, managers, medical staff, etc; not entertainment or revenue (though these would be secondary goals of course).
If a tournament like this existed we would lose a heap of players to overseas (mostly PI players, their passports are more hireable than Aussie ones) but we'd gain heaps more. The original ARC was still influencing recruitment decisions until last year or the year before.
I'd have no qualms with a 21 year old getting noticed in the ARC, learning the trade of a full professional in Japan or French D2 for 2 years, and then coming back to prove himself in Aus.