This is exactly the problem - hence why there needs to be a consequence, if there is an 18th/19th man for HIA only, I’d say that anyone ruled out for HIA has to have 10 days off playing and training - that way it shows we’re absolutely doing the best we can to stop long term HIA impacts (and helps with any future law suits), and stops players/clubs being happy to rort the rule for an in game advantage.
With something like that rule above, I’d say move to a 6 man bench, but can only use 4 players as standard, can only access the 5th or 6th bench player once you’ve got 2 people rubbed out for the game due to HIA.
HIA is different to normal injuries, as the rules are forcing them off the field, any other injury, the players choose whether they’re able to battle through the pain or not, and we shouldn’t go away from that toughness being part of the game, apart from HIA’s.