Wlad beat better opponents, but Johnson probably has more wins over world class opposition. The situation is complicated by the fact that there were not rankings during Johnson's era, but if there had been, I suspect that his stats would be pretty impressive.
Then we are comparing eras. And frankly, Wlad's era, in a head to head sense, destroys Johnson's. Historically, there are few heavies, if any, more important than Johnson. And he wasn't only important, he was really good. So, if you factor the historical angle into it, you have an argument.