" I'd certainly avoid anything that's cereal-based, picking something that lists meat, or fish, as the first ingredient. And avoid anything that's high in protein. "
can't have low protein food that is not High in carbs. Whether the carbs come from grains or pototoes,legume, tapioca etc make little difference. There is a reason carbs are not listed on the analysis on a bag of dog food it is because dogs do not need carbs.
Totally disagree on a low protein food. In an active dog higher protein level have demonstrated to reduce soft tissue injuries and there is no know harm from a high protein diet, except in late stage renal failure.
When it comes to food it is a very individualistic thing what works for one dog often does not work for another. If you like the result you are getting with the current food no need to change if not try something else there is no magic bullet.