If there were a National primary, then the proportional argument would have merit. But, we have individual state by state elections for delegates (exception Colorado where a vote doesn’t matter). Mid stream, it isn’t unusual to see the proportional issue (or lack there of).
Usually, the vote and the proportional delegates does end matching up when all states have been accounted for.
He's essentially picking and choosing the rules he likes, and those he doesn't. But in the aggregate, his delegate count certainly represents fairly the amount of votes he has received under those rules.