That's not quite what happens though is it? If a side is relegated most of their usable players end up with other lower table clubs including the promoted side, meaning almost the same set of players just at different clubs.
Whilst the cap may be aimed at levelling the playing field, its never going to because the gap between 'big' and 'small' clubs in financial terms is enormous. Even in the supposedly more equal NRL, some teams are just bigger than others, and from a commercial perspective far more important - the Broncos dwarf every team in almost all financial dimensions (in some ways the gap is even bigger here because its hidden by the TV deal which enables all clubs to get close to spending the full cap).
Failure to recognise these disparities is a mistake. I still think it was a huge mistake to let the Bulls fall out of SL and end up where they are. They didn't get everything right, but they could bring crowds that are just a dream for most SL sides, and if we're being honest SL lost something when they went. Replacing the Bulls with the likes of Leigh or Widnes isn't like for like in anyway at all, regardless of how 'fair' it is. Even in a player development sense they were immense - half the Brits in the NRL came through their Academy.
Given the current setup and teams in SL and below, there are really only 2 teams P&R helps - Leigh and Widnes. If the game was purely about financial strength it would be a continual yo-yo between them Salford and London. If we moved back to franchising Toronto, Toulouse and London would all stand a much better chance of getting in than through P&R, assuming they have the initial financial backing required.