You normally have bigger problems with water cooled bikes, if an aircooled bike overheats then it normally overheats the carbs too and the whole lot shuts down till the temperature drops.
That is in the extreem, why not ask any of the experts when they last actually experienced first hand an aircooled m/c engine overheat, 99% of the time it will be owner abuse, or neglect. The aircooled bike has no water pumps to fail, no seals,hoses,rads.
When they are in traffic they all suffer, not all bikes have cooling fans, my TDR certanly doesent so that is at a dissadvantage due to the engine not being able to shed enough heat on its own. A good aircooled engine should idle indefinately.
There are 2 benefits to the cooling system,
1 closer engineering tolerances, the aircooled motors have more expansion built in to allow for the heat generated. The poroblem there is that means bearings are not as tight, pistons, rings etc are not as snug and hot spots cannot be so easily controlled (like Suzuki deliberately cooling the bottom of the exhaust port to prevent detonation on the RG) so the aircooled engine will generate less power as a result.
2 Noise, the water jacket around an engine keeps it quiet.
Other than those main benefits, realisticly water cooling just adds weight and complexity. There are fringe benefits like carb heating but the main point is air cooled, water cooled makes no odds.
Maintanance and riding the bike within its mechanical limits (unless its a Z250) kills far more motorcycles ( ask any teenager).