George Foreman Says Floyd Mayweather Can't Be Called Best Ever, Here's Why

[[tmz:video id="0_fawc4jlz"]] Floyd Mayweather ain't gonna like this ... George Foreman tells TMZ Sports it doesn't matter if Money goes ANOTHER 50-0 ... he'll never consider him the greatest boxer of all-time -- 'cause he ain't a heavyweight! "If Floyd…