I think you are both underestimating the French, Austrians and Russians and overestimating the power of the British and Germans. I would not go so far as to say that Germany and GB could not have won this war (although that is debatable) but to say it "would not be a very close fight" is ridiculous.It began in 1913 with France demanding Alsace-lorraine. The only Nations that could realistically put up a fight were Italy and France, the latter of which would be fighting on 2 fronts. Russia, A-H, and the Ottomans would not fair well. Germany and GB were really powerful back then, Britain with its colonies and Germany with the industry, against a bunch of backwards serfdoms, and two states with two front to worry about, would not be a very close fight.
I'll start with your Entente, France is a major power with an army roughly on par with Germany's, though Germany does have an edge, and you say they'll be fighting on two fronts? Are you saying is Britain going to try to do the D-Day landings thirty years early? I find that more than a little implausible... Next Italy, firstly I do find ironic that Italy, a country known for military ineptness, is one if the countries that you have putting a fight. Secondly, with Italy being back from the front line, they are now going to be a manpower pool for the Entente to ship troops from to the front line and with the combined navies of Austria, France, Italy, the Ottomans and Russia in to Med. they will be able to do that as they please. As for Russia, they have a colossal manpower and with Germany fighting on THREE(!!!) fronts they will be able to use that to full effect, unlike in OTL. And the Ottomans, yeah they are in a bad way at the time but with the help they will get from they multiple great power allies they should be able to hold back any expeditionary force the Hamburg Pact can send against them.
Lastly, and this is what most annoys me, is the "bunch of backwards serfdoms" comment. I'm not entirely sure who you are referring to but since France is one of the "states fighting on two fronts", even though that makes no sense, I'm assuming your referring to any or all of Russia, Italy, Austria and the Ottomans as backwards serfdoms. Russia is, admittedly, pretty backward for the era but they are not a serfdom and are in the process of considerable industrialisation. The Ottomans too are still backward but are not a serfdom and are also in the process of the industrialisation of their empire. As for Italy, the south is famously backward compared to Europe, and even just the rat of Italy but to call the country a backwards serfdom is a bit of a stretch. Lastly, Austria-Hungary. As this is the only possible other candidate I can think of for fighting on two fronts I won't be too harsh (though it was mentioning that both countries they are fighting against on the Balkans front were relatively easily defeated by A-H in OTL and with Serbia and Romania fighting on all sides with little hope of allied support now that will be even easier) but A-H was in fact a industrialised country with one of the largest machine production industries in the world and was also one of the first continental countries to free its serfs (in the reign of Joseph II in the second half of the 18th century).
Essentially, GB, which has no foothold on continental Europe, and a Germany fighting on all sides will have a very tough time winning this war. Its not outside the realms of possibility that they could have won but its at best fairly unlikely.
I should note though, that for all my issues with the outcome of your scenario it is a good map.