Stewart told Sport Bild: "Sebastian has more experience and is calmer than Lewis.
"It will be difficult for Lewis to turn it around because Vettel is so hungry to succeed again."
Another former F1 driver, Marc Surer, agreed: "Vettel is someone who is discouraged by a bad car, but when he has a good car, he is incredible.
"Also, with his family-driven lifestyle, he has fewer fluctuations than Hamilton."
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