... use the Amex as my primary card until I hit the $6,500 reward level, and then use it exclusively for gas, groceries, and drugstore purchases where a 5% cash back is paid out....
The problem is that $6,500 is 25% of your annual spend. You might do better with the combination of Blue Cash Everyday and Citi Double Cash. Don't be seduced by the 5% rate, calculate
dollars per year. Remember also that there are other
free cards which often offer 5% on the gasoline or supermarket category for a portion of the year. Look at Chase Freedom and Discover.