I can't say I'm convinced by this, I'm afraid. I'd suggest that popularity is a universal gauge of popularity, and that's all (not necessarily a Bad Thing, but not a reflection of talent, nor anything else...). I'm not sure that Bach's popularity, either in his day or the present, changes anything concerning his talent. True, talent has no objective yardstick that I'm aware of, but why does one need objectivity, anyway..?