Guillermo Jones. A serious underachiever who handed out some beatings while out of shape and past prime.
Holmes is a tailor made answer for this one. By his mid 40s, he was fighting fat and out of shape with not much left other than his skill, ring IQ, and experience, and still doing fairly well. I think Foreman isn't quite as good of an example here. He'd kept his strength and power, corrected his prior conditioning issue, and somehow became more durable. All he really lost was foot speed. He never had much hand speed anyway.
Past his best days he beats D1ck Tiger whom is about to win the LHW title. Years down the line he still goes on to give Carlos Monzon his toughest fights. Ridiculous.
Unique case with Foreman in his second career. He didn’t have the wear someone like Holmes did for example.
Holyfield, he'd already been badly squashed by Bowe before beating Iron Mike. Won the title again after that...twice, actually.
Foreman stands out a little, but he lost to Holyfield and Morrison and others.. Hearns did beat Virgil Hill and had a winning record, which people overlooked, but he did fight lesser guys after losing to Barkley in the rematch. He or his handlers knew they didn't want too many tough guys past that point.. He still beat some good fighters and tough guys like Nate Miller.