Eubank dominated for large periods of the fight, dropping Williams three times during the opening four rounds and a fourth time in the 11th.
While the 32-year-old prevailed 116-109, 116-108 and 117-109 on the scorecards, the Englishman feels that he could have ended the fight earlier had he wanted to.
Speaking to Sky Sports, Eubank said: "I wanted to teach this man a lesson. He had said some menacing things to me leading up to this fight so I wanted to punish him. I thought: 'I do not want to knock this man out in the first round'. I want to get people like him out of boxing.
"You saw the fight - headlocks, headbutts, crazy stuff. I'm surprised he didn't get disqualified. I punished him like I said that I would do."
Eubank, who improves to 32 wins and two defeats, will now look to fight for the world title later in 2022.