Vettel trails Leclerc by 19 points in the Drivers' Championship and the Monegasque also leads on race wins, two to one, as well as pole positions this season. At the last race in Austin, Leclerc extended his advantage after the German retired from the race.
The battle for supremacy at Ferrari is set to go down to the final race of the season, but Irvine isn't surprised to see Leclerc leading.
“I said at the start of the year, and everyone went a bit crazy, that Sebastian Vettel was a sitting duck,” Irvine said in an interview with Betway.
“I thought Leclerc had a good chance of beating him because I don’t think Vettel is a worthy four-time World Champion.
“I think he is a very good driver, but he makes a lot of mistakes and I never really thought he was that fast.
“We are seeing that this year. We saw it with [his season against] Daniel Ricciardo and we’re seeing it again now with Leclerc.
“Vettel got an amazing deal with Ferrari. I was surprised that they took him because it was at a stage where he was getting destroyed."