No. You shouldn't give equity now based on an imaginary look-back from the future, because it is impossible to predict the future, that's my whole point. Perso

No. You shouldn't give equity now based on an imaginary look-back from the future, because it is impossible to predict the future, that's my whole point. PersonB may contribute later, but at that point there will be a lot of existing value already, hence, even if they add more value, the percentage of value they add is less, and the risk they take is a lot less (since there is already value there), hence they get a lot less equity. How early you join makes ALL the difference.