I agree. The war with France alone might have some successes and build things up for TTL Edward III. With extensive Gascony holdings, this should be a much easier war. It should be noted despite the discrepancy in population, tax base, and army size the Plantagenets nearly won the HYW since it was a civil war as much as a war between kingdoms. At one point Henry VI's regents actually had three times as many non-merc French (levies from Normandy and loyal counts) as they had English in their field armies in France. Once the momentum slid the other way, the French counts suddenly left the Plantagenet camp and all lined up behind the "right" claimant, but if TTL Edward III gets a head start, it shouldn't be a Hundred Years War. 30?
That may be true, but the Hundred Years War as we know it would be directly butterflied.
See, the reason for the war was because the Direct Capetians became extinct, and the throne went to Philip VI, who was the first cousin in the male line of Charles IV. Edwards III was the nephew of three French kings, Louis X, Philip V, and Charles IV, because his mother, Isabella of France, was their sister, and a child of Philip IV, while Philip VI was merely the nephew of said Philip IV.
In this timeline, since Edward II marries the Maid of Norway, and this Edward III would be the child of Margaret of Norway and Edward, it means that Edward II does not marry Isabella of France, and this Edward III would not be the grandchild of Philip the Fair, and thus, would not have any claim on the throne of France that is better than Philip VI.
And without any claim to the throne, there is no basis for the war as we know it. Any plausible war would be on the status of Gascony, which, as the War of Saint Sardos shows, and all wars since the time of King John, goes badly for the English. Why? Because the other French nobles would not support the English king, because they could not pretend that he is the rightful king of France, and therefore, not violate their feudal oaths.
In OTL, the supporters of the kings of England in France would say that they are not rebelling against the king of France, their rightful overlord, but merely supporting their liege, the rightful king of France, who happened to be the king of England. In this case, there would less ideological justification of supporting a rebellious vassal against their king.