Francis has posed interesting points:
Let's consider these points. Seizing the French Fleet. German troops don't go anywhere near Toulon in Southern France where the mainland ships are located. But they don't need to, they simply order the Petain government to hand them over, like the tanks. Petain's government is the legal government of France. Petain is not a puppet imposed by the conquerors, like Quisling in Norway, but the appointee of the French head of state President Lebrun and authorised to get a deal, at pretty much any price, to get peace to save French lives, military and civilian. If that means reneging on a promise made by the previous administration to the "perfidious" British (who wouldn't deploy every single soldier and every single aircraft in France to save France), so what? France is beaten, the ships are no use to her, and letting the Germans have them to stop the killing would make sense. Mussolini demands some as well. Gallic Shrug. Realpolitik. Those in command of the ships have no reason to disobey orders given by their Government. These concessions would mean French men and women get to live. No-one expected Britain to fight on. It is alleged the last French army commander who oversaw the collapse of resistance said:Do you assume that Germany and / or Italy seize the French Fleet or that France goes to war against Britain ? These are two different situations. If France declares war to Britain (it's very unlikely IMHO, but let's assume it for the sake of discussion), then the problem largely bypasses the domain of naval warfare, and there IMHO are too may variables to continue the discussion.
After Oran and later Dakar, Laval and other important right wing Frenchmen might easily have persuaded Petain to throw in his lot fully with the Germans as an active ally. Especially as with Stalin co-operating closely with Hitler, even the French communists had no axe to grind. Uncle Joe would surely approve. French bombers attacked Gibraltar on two successive days in September 1940 as reprisals.Maxine Weygand predicted, "In three weeks, England will have her neck wrung like a chicken."
A lot has been made recently, in some circles of the Regia Marina's success in getting supplies through to North Africa, without acknowledging that since the shortest distance Messina to Tripoli is only 340 nautical miles, it's frankly pretty easy. Even with diversions it certainly doesn't compare with escorting convoys lengthways through the Med to Malta or Alexandria. Some are very keen to claim credit for the Italian Navy when actually German and Italian aircraft operating from Sardinia, Sicily and North Africa, together with a handful of German U-boats scored many major successes. It was every bit as important for the Italian Navy to pull its weight in starving out/invading Malta and stopping tanks to Alexandria in aggressive moves as well as simply covering a few quick trips to North Africa. Taranto should have provoked them into action not added extra levels of caution.
Sure, there are points to criticize in some French vessels but all ships have their shortcomings. The British Counties were Tinclads, as were Renown and Repulse. The R Class battleships and the Nelsons were too slow to even catch a cold. The British put great faith in 1940 in getting their hands on 50 clapped out old destroyers from the USN, how terrifying was the prospect of Raeder getting his hands on some or all the French Navy for an invasion of Britain or strangulation in the Mediterranean?
For Paul: Prince of Wales and Rodney went to help in the Mediterranean on Operation Halberd in September 1941 even before loss of Ark Royal and Barham to German submarines. Even after Taranto losses the central strategic position of the Italian Navy gives them considerable advantages over British forces spread out in Gibraltar and Alexandria, if they had adopted the initiative. I am not sure having extra ships would help. I don't suppose some French ships manned by the survivors from Blucher and Bonte's destroyers in 1940 under Raeder's orders would have been so passive.
Good news is, Darlan was able (allowed) to keep his word. So it's all hypothetical.
All the best