Only Leeds, Bradford, Wigan and St Helens have won the decider since the competition started.
“I have been really impressed with Hull FC,” he told Love Rugby League.
“Lee Radford has done a terrific job – the recruitment over the past 18 to 24 months has been great.
“You also have to commend Gareth Ellis for his leadership of the team.
“Warrington are another side which have threatened and come close over the years so it’s only a matter of time before they win a Grand Final.”
Sinfield retired at the end of 2015 but has kept a close eye on the fortunes of his former club Leeds.
“The start of the season was pretty tough. To lose Danny [McGuire] in the first game was hard.
“Some clubs were gunning for Leeds after winning the treble so the poor run of form played right into their hands.
“In recent times, some of the performances have been brilliant. It’s just a shame we have found our form a bit late.”
Looking ahead to the upcoming Qualifiers, Sinfield believes Leeds will do well but they can’t afford to take anyone for granted.
“I think they have a really strong chance in the Middle 8s,” he said.
“It is clear that when everyone is fully fit, they are capable of beating anyone.
“For me the full time clubs will have a much better chance.”