Earnie Shavers vs Ray Mercer

I don't think so.

Mercer was schooled by a 42 year old Holmes almost as bad as Shavers was schooled by a 28 year old Holmes.

Shavers lost to some journeymen, but Mercer lost to Jesse Ferguson, and "drew" (a gift) with 7-9-2 Marion Wilson.

Shavers has best wins over Ken Norton and Jimmy Ellis, both 1st round KOs.
Mercer's best wins are Francesco Damiani and Tommy Morrison.

So, no I don't think there's any reason to find "two levels" between Mercer and Norton.

 

Mercer by KO in 4-6