If CTE (and other related) is such a no go how does WWE, UFC and other martial arts contests survive? Two ways. Firstly they have clauses in their contracts that specifically indemnify the organisers against litigation. Secondly, it's pretty difficulty for a martial arts fighter to say he didn't know that he was going to get hit/kicked/punched in the head. He competed knowing full well what was going to happen and that he was risking CTE.
The problem with CTE in the NFL (for example) was that the NFL denied it, covered it up, told the players that they would be just fine, nothing to see here. As usual it's the cover up that results in the litigation, not the act itself.
The NRL have been pretty smart in admitted that CTE is a problem and has taken steps to minimise it, but it will never be eliminated, NRL is a contact sport after all. The players know this, they sign contracts, they continue to play, they take on the risk themselves. Yes there is history, older players suffering, but the defense is that medical advice on CTE is only recent and no one really understood the consequences of repeated head injuries. Now they do and they are taking action to minimise it.
Always a Bulldog