So Tim Scott is supposed to win a GOP primary against another Trump fake populist clone running as well?
The GOP's base is not mainly motivated by populist politics, it is the racism/white identity politics that gets them to the ballot box. This was true of 2016 GOP primary, the 2016 General, and it is probably true of the 2020 General.
All you are saying is that a moderate Republican (especially if black) will be difficult for a democrat to defeat in the general, but that has been true for a long time.
The problem is, moderates can't win the primary.