The singer's comments come after after Dalton Harris, 24, was crowned winner in the final after being mentored to success by Louis Tomlinson, reports dailymail.co.uk.
Simon Cowell's act Scarlett, 21, finished as runner-up and another of Tomlinson's acts, Anthony Russell, 28, came third.
Williams said how he would have had his act Acacia & Aaliyah, who were eliminated in week six and finished in fourth place, sing different songs if he had been there with them.
He told The Sun: "Had I been with them maybe I wouldn't have had them perform Maniac. But from South America it's difficult to feel the temperature of the performance.
"I watched it in Guadalajara in Mexico thinking, 'I wish they hadn't done that'. That's down to me. My not being there cost them, I think. But I'm delusional and think I'm going to win everything, which is how I've got this far - delusions."
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