Not only that, but the hundreds of thousands of Austro-Hungarian troops deployed against Italy IOTL could be deployed against Russia ITTL.
True, but I left this out because the war might be over, and would be won before the impact of this begins to be felt in May 1915. Remove a French Army from the German front, the Germans probably hold at least the Marne line and have a sporting chance of taking Calais. A lot will depend on how well things go in France. If France is driven to the peace table by the end of 1914, then it is a quick war. If France makes it to about May 1915, then Germany will still need to turn east, so it will be the decisive campaign of 1916 that ends the war.
No Gallipoli only means the Entente avoids that extremely costly fiasco which is to their advantage.
As for Italy once the RN destroys Italy's coastal trade which is effectively the Italian economy south of Rome...
Yes OTL, Gallipoli was a mistake by the UK. If I was writing a TL to have the Entente do a lot better, cancelling Gallipoli is very high on the list of POD. IMO, if the Gallipoli forces are used in France, the UK might actually break the German lines, and at a minimum, they forces Germany to abort its attack on Russia 1-2 months earlier. This is partially offset by the Ottomans doing better, which will not be felt in 1915 to any large degree.
However, in a war with Italy on Central Powers side, it will not work out so nice for the UK. By late 1915, the Gallipoli forces will be merely replacing French units tied down fighting the Italians, and likely the war is over in early 1915 in a negotiated peace. However, if it goes on longer, the Ottomans become a real issue for the Entente. With only minor Italian/A-H forces in the Black Sea, the Ottomans will be able to conduct landings against Russia exposed coast line. For Example, the Ottomans attempting to retake the Crimea combine with a stronger than OTL attack by the Germans into Russia might well collapse Russia. If the Eastern Med can be contested, then Cyprus and the Suez come into play. If the blockade is loser and more railroad material becomes available, the Suez and Basra come into play. Even if none of this happens, the Red Sea will come into play. The Ottomans need just one short Spur to make the Red Sea a major naval battleground area.
Yes, if the RN deploys heavily to the Med, it can make life very difficult on Italy. Italy has a huge coal issue. Libya will be a problem for them But I am not sure the RN moves many more ships to the Med than OTL due to the existence of the High Seas Fleet, and with OTL deployment, who wins control of the Med is not certain. To a large extent; the French, A-H, and Italian Navies are untested in major surface actions. Many items that we know about the RN from Jutland are still unknown for these Navies. For example without Jutland, few if any would know how bad the BC ammo handling policies were, and few would understand how bad the UK's newer ammo was.
From the Naval perspective, it would be a great TL to read, but without sticking it in the ASB section, the land battles would move so fast, the naval war would not have time to develop.