He's the best of his era, and therefore quite naturally will go down as one of the greats.
I don't think he's ever beaten a great fighter, though. That's why I think it's quite speculative when people say he'd beat anybody that's ever lived on the strength of his victories.
The smaller greats like Ali, almost certainly he would as there is no bridging that gap with skill and speed. But greats like Lewis, Holmes that are big, athletic box-punchers are a very different proposition to Robocop Wlad. Also, if you look at somebody like Foreman, even though he was considered rudimentary in his skills, his delivery of that power is FAR more effective than Deontay Wilder. Wilder very nearly had Tyson out, so that's no easy night.