how can it be a restraint of trade I think if it was that easy then the nrl clubs would have done it salford broke the rules of the comp and not just by giving someone a car they deliberated payed tp from another company and didnt declair it

The opposite way to look at it is would an increase in salary cap, or the removal of the salary cap affect any of those issues you mention above. Without a salary cap at all players wouldn't move clubs either- because a handful of clubs would have all the money to spend whilst the rest had to make do with what was left (see Wigan circa 80s ). Would a higher or non existent salary cap encourage new players to play RL or in reality would we just be paying the same players more money. Would young British players be more likely to be involved in the sport or less likely whilst clubs bring in star names from the Southern Hemisphere or RU.
You could be right in that the salary cap doesn't promote those things-you mention above, close competition, new revenues etc etc but equally those things may not be promoted with no salary cap in place. It wasn't prior to.

Maybe so (I don't agree but....) but you do need to justify having a restraint of trade. You don't need to justify not having one.

The 1994 major league baseball players strike was because the owners wanted a salary cap that the players union refused to accept.
It ended after many court, Congress and even then president Clinton interventions with the owners being forced to withdraw the suggested salary cap and replace it with the luxury tax that still exists today.
In fact only NFL and NHL have a full salary cap in place the NBA use a mix of salary cap and luxury cap.
For those that don't know the luxury tax system basically it works by allowing clubs like the Yankees to spend over a set limit by however much they choose but for every 1$ over they add another $1 to a central fund that's divided amongst those clubs that can't spend up to the limit.

Their argument would be solvency- however......

That's not the full story though - the MLB also uses a revenue sharing system, which takes a % of net local revenue into a central pot, and divides it amongst all teams in the league. This is aimed at assisting those clubs who don't have a large local market, to stay competitive with those who do.

As I said - a SC in and of itself is unlikely to be ruled as unlawful; but the RFL could do a much better job of implementing their SC - and there are examples for them to work from if they were so minded.