Yeah theres a few exceptions for sure. I wouldnt give him much hope against many of those that you've mentioned in the middle rounds he was a small heavy. I dont rate him either, I think he cheated with alot of his shots being off the padded area of the glove too.
Wore men down.
Generally again, I dont know how many modern fighters could continue into 15 rounds with some of the men of old either. Most look good when they are getting everything their own way but they fold much faster these days when they dont, I dont think they have as much grit put it that way.
Its a varied thing on too many levels, size, technique, rounds even the latest in footwear would have most modern fighters moving, gripping and hitting harder.