I'm sure some people already replied to this, but Germans (and especially BMW) are known to underrate their own cars, there's plenty of dyno runs out there where it's pushing out past 500hp.
So something like the 473hp on the M4 is actually that to the wheels or even more, while something like my 480hp Bullitt is I believe 410-420hp to the wheels.
Your Bullitt is probably closer to 440. Non Bullitts are in the 420 range. I agree, the manual M4s are hitting 120+ in the traps at almost 3800lbs.