The HD200 is water-cooled. I own two of 'em. Had to clean the cooling system on both. The OEM coolant is pretty sleezy so if ya don't purge it when the bike's new you get a lot of scale.
Ceramic coated piston and a four valve head too.
Far as air-cooled longevity goes I'm not referring to the exceptions I'm referring to Joe Average. for lifespan without not able (if simple) rebuild work.
Their longevity depends on where you used them, & how you maintain them.
In town stop & go in hot environments were a bit tough. This is true of water cooled as well but they do take rough use better.
Keeping the windshield clear in cold environments is tough too. The water cooled engines do great in that regard for the most part (Yugo's/Fiat 128s...notsomuch)
I worshiped my old bug motor and drove delivery in the Twin Cities with it. Took a lot of love and a lot of valve sets vs. the Datsun 210 that replaced it
The Datsun & later Corrollas (RWD old ones) took the beating better with less maintenance & delivered better MPG with cleaner emissions.
All that said I still love air myself, & would love to have a 71 bus with vanagon brakes, but those are a bit thin on the ground these days, & getting a mite pricey for nice ones in addition to my lack of space for said since I would not use it as a daily driver..
Far as scoots. I did use an air-cooled scoot as a daily ride. The HD just plain did a better job at it. To bring it up the scale compare a water cooled bike like the NT700 to a Harley 883. The Harley has some charisma IMHO, but in terms of the motors it's unfair to the Harley. Heck my 638cc burger, inefficient transmission and all womps the 883s & the 1200s
All that said to each their own so ride whatcha like. If I had my way and space I'd be rivaling Leno & ride what suited the mood.
Yeah, the Jet 14 (looks like a PCX) and the HD200 (ST200) are both 169cc air cooled motors.
Bubble and squeak is essentially the leftovers from a roast dinner in batter.
Bangers and mash is sausages with mashed potato and gravy. Yum.