@@dtxspeaks268Vader would have probably just grabbed the ship with the force and crush it. Going all out on the weapons puts him on the back pedal and gives him a shot to possibly get Anakin off guard
They had just lost the war and had nowhere to go. Even Cato Neimoidia, his homeworld, had fallen to the Empire. He had no flagships either, but even if he did, it would have been attacked and destroyed eventually.