Thats a bit of an odd comparison as they are in pretty different categories and don’t really compete against each other.

There is exactly one actual ocean liner left, QM2 which goes between my home city and New York. Most of the ships you're thinking of are Cruise liners, which are not in fact (unlike an airliner or ocean liner) designed to prioritize travel but are instead floating hotels which might happen to travel from one place to another.

Ocean liners use several times more fuel per passenger mile than airliners.

So what? Two things can be bad at the same time. Nobody mentioned ocean liners except you. Why not bring up the greenhouse gases from landfills while you're at it?

Whatabouting everything is so last decade.