Earlier quoted context omitted.
I think the prevalence of concussions in football compared to rugby is proof that "better equipment" doesn't prevent concussions. It has the paradoxical effect of causing them. Better shoulder pads allow for people to launch their bodies without fear of separating their shoulders. Conversely, helmets are not designed to protect the brain, only to prevent skull fractures. Thus, I don't think your argument holds water.
You are right about the equipment (even though obviously only concussion vs concussion + skull fracture is a step forward!), but the difference between football and rugby goes way beyond the equipment. In the former there's no lateral passing, which means that the ball carrier will always be a target for the whole defense. In rugby you can pass the ball, which makes the defense spread wider and doesn't allow them to…
In football, at any given point and time there is one person with virtually a huge bullseye on them and it is sometimes a valid tactic to lay down a more punishing hit (cause a fumble, make a statement, scare your opponent to make a mistake or drop the ball next time, etc) at the expensive of not making a "secure, form tackle"
Ironically, if I am remembering correctly, the Seahawks and coach Pete Carroll teach more of a "rugby" style tackle, and that's why they consistently have one of the best tackling defenses.