The Dutch coach reluctantly sold the 25-year-old Belgium midfielder to Spurs for 15 million pounds last summer and his high-intensity displays have been integral in getting his new side to third in the table.
Jol - who has managed both clubs during different spells in England - believes that despite Bale being a hot favorite for various Player of the Year awards, Dembele is the true star of Andre Villas-Boas' side.
"We wanted to keep Dembele," Jol told reporters. "You can give him the ball and he won't give it away because he is too strong - even if there is no time and space.
"Spurs are strong. The nucleus of the team has been the same over the last few years so they can't be a one-man team. Bale's making a difference. But on the ball, pound for pound, Mousa is probably the best."
Spurs' win rate with Dembele in the team is an impressive 68 percent, winning 15 games while drawing two and losing two, but without him the win rate plummets to 14 percent, with one win, two draws and four defeats.
While Spurs narrowly qualified for the quarterfinals of the Europa League after going through against Inter on away goals (4-4 agg) at the San Siro on Thursday night, Jol doesn't believe fatigue will be an issue for his former club on Sunday.
"They have a big squad," Jol said. "If you rest five or six players, like they did at Inter, there is no problem."