Could a stronger Force Z have changed Allied command and the fall of Singapore?
Short answerPossibly: it could attack Japanese landings and supply lines, complicate the Malayan campaign, and support a British-led Southeast Asian theater.
NotesAn operational carrier group could harass the Japanese advance down Malaya and make the fall of Singapore less certain. If Japanese land forces could not sustain themselves by sea, the effects might extend to the Dutch East Indies. A surviving Allied naval concentration could also change how the Southeast Asian and Central Pacific commands were divided. These are linked possibilities rather than a guaranteed reversal.