Ok, first thing, the AP gap is still considerable, with Jin being more than 4 times stronger than Siegfried and this is a major factor.
Siegfried can use Soul Charge to fill the gap a little bit, but we have no evidences it would be significant. But his greatest advantage is surely being a swordfighter with higher range, while Jin in base has only his fists. Electricity and fire are useful, but Soul Wave is resisted.
In terms of experience Jin should be advantaged, as he already mastered the Kazama karate, entered several Tekken tournaments and defeated great fighters and monsters, but he never faced a medieval knight and his giant sword, although he might have went against Yoshimitsu, but there's no proof of that.
On his side, New Timeline Siegfried spent several years facing opponents that were hunting him for revenge, although no one was like Jin, and eventually defeated Nightmare.
Overall, I think Jin would be able to take this most of the times. The moments he get in close distance he's going to destroy Siegfried with his much higher skill in hand-to-hand combat, LS and AP. Siegfried surely has his own chances to win, mostly due to the range advantage, but I see him on the lower side of possibilites.
