In 1939-40 the Axis stayed in the game mainly by the allies grossly overrating their strength, and the victory in May 1940 is based on a string of "lucky" events - in combination highly unlikely, but giving an unrealistic high estimation of German strength. The most likely outcome of WWII would have been the Germans bogging down in 1940, and Hitler soon after being replaced as a total failure.
In WWI both sides had their miracles initially, the Germans at Tannenberg and the French on the Marne, POD one of these out, and the war will probably end on that front very soon after. As a large part of the miracle at Tanneberg stemmed from incredibly incompetent Russian leadership I guess we all other things being equal need more and larger PoDs to let the Russians exploit a more favourable situation than the Germans need to exploit an absent mriacle on the Marne. Not that I think of German armies sweeping over northern France Blitzkrieg style, but I think the French government and the alliance with GB will have a fair chance of collapsing if the Front waver any more than in OTL.
Next question is how close the French came to collapse at Verdun, not far IMHO, and having Petain choke in a fois gras sandwich might do the trick.
In Italy the Italians until mid 1918 were closer to quitting than the Austrians - imagine the Italian government panicking in October 1917 (perhaps sans a brutal Cadorno to stop the rout) and quitting alongside the Russians. On top of some added pessimism on Entente side, that might give the 1918 spring offensive the extra ompfh to roll up the Entente in France. Although the Austro-Hungarians had their trouble with some unit's loyalty and enthusiasm, it would not be difficult to find say 30 high quality Divisions and add them to the 1918 spring offensive in France.
The biggest Entente chance IMO lies in Russia. Either a more competent Russian leadership in 1914 or a better planned and executed Gallipoli offensive in 1915. If the Bosporus is opened to Entente traffic, the Russian army from then on will be quite another matter than in OTL, and I doubt if the CPs can hold on.
But all in all, and IMHO, where the CP in WWI had close to 50-50 chance of winning, the Axis in WWII hardly approach a 20% chance.
Regards
Steffen Redbeard