They did more than just shake the universe; the destructions were stronger the further away the shockwaves got from both Goku and Beerus. More importantly, neither nor Beerus were even close to using their full power; or at least it's true in Beerus's case. Goku was however getting stronger and stronger as the fight proceeded, proof that he has yet to tap in to his full potential. Also, they shook the universe twice; and it was confirmed the third time would have completely destroyed the universe they were in. Even if we lowball this feat, it would be 3-B at bare minimum, but as Knight mentioned, they also shook and would have destroyed the afterlife, which is much larger than the universe. So even at a low ball, cutting the feat in half would still be above the baseline for 3-A.
Additionally, Goku and Vegeta later trained to the point where even their base forms surpassed what SSG Goku was at BoG saga; on top of the fact that they could still go SSJ, SSJ2, and SSJ Blue with each form being significantly stronger than the last. Bottom line, DBS Goku is far above the baseline for 3-A. Hope the info was helpful.