I agree with you about the greatness of Ezzard Charles but in regards to MM being the 4th best LH in his time I do not agree. We simply don't know what would have happened if he got the opportunity to fight Hill, Maske or any of the other top guys. I don't care much about those rankings to tell you the truth. Bottom line they never fought to decide who was the best.
Probably Moorer who was much bigger and more powerful. Moorer had a suspect chin, it wasn't an issue prior to moving up to heavyweight. Moorer's skill set is rather under rated. He was good enough to out box Evander Holyfield, and was having an easier time vs Foreman than Holyfield or Morrison did until he inexplicitly got caught looking down the barrel of Foreman's gun.
Moorer, possibly by TKO/KO and mainly attributed to the size advantage he would hold over Ezzard but also due to him possessing just enough wit to hold his own in this match-up IMO.