Fleet Air Arm aircraft were designed for a different carrier war

How effective would British carriers and their supposedly poor aircraft have been in the Pacific in 1942-43?

They were effective within British doctrine, and would likely have mixed Fulmars, Hurricanes, and later American aircraft as operational needs changed.

A simple top-speed comparison misses the missions built into British and American carrier aircraft. Royal Navy carriers in the Mediterranean often faced repeated land-based attacks for days, rather than one carrier engagement followed by withdrawal, so endurance and continuous patrols mattered greatly. Fulmars could navigate at night and remain on station with a second crew member, while Hurricanes supplied short-range interception and Albacores performed strike work. American airframes could be adopted when supply and performance made that useful, though they would still be fitted into a British air-group system built for radar cooperation and persistent operations.