In my state, one votes for specific named delegates committed to specific candidates. In your system, how would the delegates be selected? Would they be appointed by the state parties? If you think there was a conspiracy to select delegates supporting a specific candidate, how would you system prevent the state parties from conspiring?
If 50% were required to get delegates committed to one’s name, then we would not have this steam-roller effect that comes with someone winning an earlier state by a small margin and using that victory to launch past other candidates in the mind of the media.
In fact, this system could reject ALL the candidates. That would have been a good idea this year.
And selected local delegates at a national convention could probably do a better job of picking a candidate as do popularity contests in each state. Representative democracy....the republican ideal.
Nonetheless, the popular vote could still win for a candidate IF some candidate were the clear choice of the majority of primary voters.
Otherwise, no way the candidate should be someone unable to win in state by state contests.