Exactly. In such a long-term game you can't announce new rules redefining the whole strategy and apply them directly.
Even more when it's about something that EVERYONE hates and that makes the game unfair : injuries.
Right now a 9+ stamina player will play 45+ min in every tight game. And because of his high stamina, he should end up injured more often ? That makes no sense.
Why not just lower even more the efficiency depending on stamina and playing time, and allow more substitutions in tight games for high stamina players ?