All of the foods with 6-stars are there because they have high meat content and no grains whatsoever. It has nothing to do with the protein content
Your expert is a bit behind the times, I think. It is increasingly accepted now that it is not "high protein" that causes behavioural problems and hyperactivity, but high amounts of carbohydrates and sugars (just the same as for hyperactive human kids, surprise!). The best thing for a hyperactive or aggessive dog (in dietary terms) then, is to ditch the carbs and go for a high quality protein food instead.
The end result is exactly what you're experiencing - a calm and relaxed dog. What more proof do you need? LOL