First are you talking about Wind forecast with is the averaged wind over 10 minutes or about Wind gusts (rafales in French)?
Do you have a mean to measure locally the wind speed?
And which model do you use in Windy? There are 7 models available in your area and it is better to compare them.
Near the Porquerolles island there is the weather station of Hyères airport (at 11 km). I do not see such big discrepancy about wind that you mention.
Here is the comparison with the Observation vs forecast tool that you can use yourself (select Reported wind and click to a weather station). There are not such big discrepancies about wind these last days with all the available weather models.