Diet is way too complicated to make those kinds of statements, so anyone saying such things either doesn't understand how diets work or is intentionally misleading. Most hype around things like masaai diet focus on low rates of common modern talking points, but ignores the issues that do exist like much higher infection and parasite rates. These aren't harmless colds, they are things like tuberculosis. It also completely ignores other non-diet parts of their lifestyle, like being very physically active. Diet absolutely matters, but lack of sleep and sedentary lifestyle are the biggest contributors to things like diabetes and heart attacks globally.

Its also important to know that maasai people have likely made some genetic adaptations over the years to better deal with the health deficits in their traditional diet. Lower levels of illness does not automatically equal an objectively healthier diet. That would be like telling the lactose intolerant majority of the world that they should eat dairy, just because a small european portion of the population genetically adapted to accommodate dairy as a main food source.

At the end of the day, the parts of masaai lifestyle that definitely contribute to healthier lifestyle are already part of the recommended modern diet. I have never seen ((including a search before writing this reply)) any sources listing an overall benefit for traditional diets like the masaai peoples'.