What about Todd Hamilton? I haven't heard of him since he won the British in 2004.
He has 2 PGA Tour wins, the 2004 British Open and the 2004 Honda Classic earlier that same year. However, he's won about a dozen times on the Asian PGA Tour. Micheel and Beem are worse than Hamilton.
Orville Moody won the 1969 US Open, and that was his only PGA Tour win. However, he spent most of his early life in the military, and didn't start playing professional golf until he was in his 30s. He also won several Senior Tour events, so I think Beem and Micheel are worse.