Reading his record is enough and it makes it fairly obvious. This discussion has been done dozens of times in here. There's an outstanding search button, you should try it some time.
Vitaly and Holyfield are better wins than any in Holmes's resume. Lewis sees Shavers, Norton, Weatherspoon, Cooney, Weaver and Williams and raises with Tua, McCall, Morrisson, Mavrovic, Briggs, Botha, Rahman, Rahman, Ruddock, Golota, Bruno and so on. I don't even count the Tyson win, even if Mike had more of a pulse than Ali when Holmes beat him. Lennox beat every man he faced. Bowe refused to fight him. An undefeated, proven guy like Akinwande was scared shitless in the ring with him.
It's not that complicated, really. Still, the gap isn't huge. You're entitled to have your own opinion. And to use the search function.