Your assertion that an MBA is an "EXTREMELY STRIPPED DOWN" version of the undergraduate is not true. Similarly a Computer Science master's program is not stripped down compared to an undergraduate CS program because it lacks "intro to data structures" and other such classes.
Also be aware that there are Executive MBA programs (EMBA) that are somewhat stripped down compared to a regular MBA program. EMBA programs are designed for people who are already in some sort of senior management position. In other words some traditional MBA classes deemed redundant given their work experience. Check with your brother to see if he was in an EMBA or MBA program. Also, things can vary wildly from school to school in terms of academic expectations, difficulty of classes. Its really only safe to compare undergrad and MBA programs at the same university.
And yes, "mustangs" are generally the best.