I don’t think concussion rate is the right metric. Football’s CTE risk is supposed to be from the incidental head to head contact that happens every play.
You are right, it isn't a perfect metric, but it is the best one we have until further studies are done about sub-concussive hits. Measuring hits like that would change the relative rankings of the each sport (soccer probably becomes more dangerous while baseball less so), but the overall point still stands that most sports involve some risk of head trauma.