I think you are probably right technically - BUT - with the responsibility for player safety in mind... if (theoretically) a player is stumbling around the pitch after a head collision, and it was so obvious to me he was unwell, and if the team refused to treat him or sub him I would stop the game and insist on treatment and not allow the player back on. I’m with you as I’m struggling to tell you where in law I’m entitled to do that but I have no problem making up a law or stretching my interpretation of our responsibility for player safety in this situation