The Wigan captain led England to their 20-18 semi-final win over Tonga in Auckland but was missing through injury a week later when they lost 6-0 to Australia in Brisbane.
As O’Loughlin prepares to bring down the curtain on his 19-year career in Friday’s Grand Final, Sinfield paid the veteran loose forward the ultimate compliment when asked if he would have made all the difference three years ago.
“Yes and throw Gareth Ellis in there, he would have been great to have out there as well,” Sinfield said.
“Sean is certainly a legend of Super League and one of the best players we’ve ever produced.
“He could have played any position on the field with his wonderful skill set and great work ethic. I loved playing alongside him.”
Former Leeds back rower Ellis, who retired from the international game before the last World Cup, has now hung up his boots for good and St Helens prop James Graham will make it a hat-trick of retirees as he prepares to play his last match on Friday night.
“The game is going to miss all three of them,” said Sinfield, who was able to bow out of Super League in 2015 with a Grand Final ring, a fairytale finish that will be denied to either O’Loughlin or Graham.
“I think the team that has the best reason to win often comes out on top but they’ve both got legends who will retire at the end of this. It’s too close to call, I reckon.”
Sinfield, the Leeds director of rugby, was speaking at a press conference to unveil details of his bid to run seven marathons in seven days from Tuesday to raise funds and awareness for former team-mate Rob Burrow and the Motor Neurone Disease Association.
Seven is synonymous with Burrow’s old shirt number and Sinfield, who will set off each day at 7am and aim to finish by 11, is hoping to raise £77,777 by the time he finishes his runs on December 7.
“Unfortunately for me, I don’t think one marathon would have had the same cut-through as seven,” Sinfield said. “I am pretty glad he didn’t have a squad number in the 20s.
“I did three in three towards the end of October that was really tough so seven in seven is going to be lot more difficult but there’s a reason for doing it.
“I have no doubt there will be some dark moments during some of these runs when you start to question what on earth you’re doing but I will be trying to remember some of the good times and funny moments that Rob has brought and shared with us all.”
Burrow, who was diagnosed with MND last December, is now largely confined to a wheelchair and has lost his speech but remains in high spirits, according to Sinfield.
“He’s fighting it as you knew he would,” he said. “Clearly some things have stopped working, he’s using his voice player a lot more now.
“But the great thing is that every time I see him, he makes me laugh. He’s still got that spirit and that sparkle in his eye.”