Would losing the Black Sea fleet impact Russia's overall strategy and ability to hit Ukrainian targets? Sure. Would wiping it out a year ago have ended the war right then and there? Probably not.
Losing Moskva was a black eye for the Russians and a nice little propaganda triumph for the Ukrainians since it was the fleet flagship, but it wasn't exactly a crippling blow. Moskva was an older vessel (laid down 1976, commissioned 1982) that had no land-attack capability, only anti-air and anti-ship missiles, and they've got plenty of other options for both. Their newer Admiral Grigorovich-class frigates do have land-attack capability, but there are only three of them, and I will bet an entire case of Scotch that for every cruise missile that they've fired at land targets in the Ukraine, there have been a dozen or more launched from mobile artillery units and silos in the Crimea or from bases inside Russia and Belarus. In fact, the BSF itself maintains an extensive inventory of land-based missile artillery, so even if Ukraine had somehow managed to Pearl Harbor every ship and submarine in the fleet, the Russians would still have more than enough land and sea-attack capability in the region to keep making life miserable for Ukraine.