The Q, as seen, can create an universe/a reality by snapping his fingers - omnipotent/beyond physical law, etc.
All the forerunner achievements you named are child's play by comparison - and certify that the forerunners were most definitely bound by physical law.
Not to mention, none of these ancient "god-like" civilizations were powerful/smart enough to prevent their own extinction. Which is more than enough to destroy any "god-like" mystique.