"It's a lot tougher transition to make than being an outside back. A finisher is naturally born for the position. You try to beat a couple of blokes and score. Being a decisive player in the team where you have to make quick calls, and step up, lead the team around, that's hard.
"It was sad to see him come back and not go as well as he hoped. Hopefully he gets an NRL team soon and we get to play against him."
Williams refused to talk about his private life in the interview to promote his signing of a global deal with Adidas - following rumours that his new wife Alana Raffie is pregnant.
But the 28-year-old did hint at the want of fatherhood and how he plans to retire from rugby in a few years.
"For me it's about putting myself in situations where I want to challenge myself. I'm 28 now and I'd only like to play into my early 30's. I want to be able to run around with my kids," he told the Daily Telegraph.
"I've had a successful career but I won't be a player who just hangs around."
Williams said it won't be easy to leave the NRL for a second time.
"It's going to be hard to leave. It's tough. When I came back last year I still felt I was a rugby union player. Now I feel like I've fallen in love with rugby league again."
The enticement of a second World Cup medal and a possible Olympic sevens medal may make the transition back to rugby all that easier.