I'm not sure. It's a mixed bag. Aircraft powerplants get torn down and rebuilt based on engine hours with no debate.
I believe there are watercooled V-6 aircraft rated engines. Do you have any example?
2500hp AA fuel engines have a fairly short life span. So do Bug engines rebuilt in the carport with Harbor Freight tools.
Possibly a level playing field is motorcycles; they come in air- water- varieties. Here's a water-cooled Vespa:
http://blog.vintagestyle.eu/ten-inch-terror-meet-the-vespa-husqvarna/