Your brain can process an astronomical amount of information within a fraction of a second. Its not about perfectly placing your head. Its about determining the potential threats angle to you and adjusting.
Ball carriers always have enough time to see what side the defender is on. If he is on my left, I lower my same side shoulder while sliding my head towards the opposite shoulder. And vice versa.
This is not easy but it is very much possible. Do you seriously think using a helmet as a weapon by attacking with the crown and becoming a human ram is good for this game?
Watch the Richardson highlight they keep showing. Its absolutely brutal for both players. The only good part about it as it happening to an Eagle. You can still lay devastating hits with your shoulder. You don't need to use the helmet.