7% is neither good nor bad. This % is just the mineral content, and a higher or low level is generally doesn't mean anything. Except in the case where cats may need to be magnesium restricted ( and you need to look at magnesium specifically), or phosphorus restricted this number is just a number.
I am not sure what Blue Buffalo is saying as they have added chelated minerals in the ingredient profile, so I am not clear as to what they are saying regarding "unlike other brands that add vitamins, minerals and antioxidants, LifeSource Bits are “cold–formed” to preserve their full potency."
Maybe someone else will have a look at that, or I am looking at the wrong food?