Can other custom/cruiser motorcycles be more desirable than a Harley-Davidson?
We all know that Harley-Davidson is one of the most traditional motorcycle makers, still regarded as a premium brand even though it's technically outdated compared to the competition from Europe and Japan. The air-cooled V-Twins with a transversely-oriented crankshaft still fitted to the majority of the Harley-Davidson range end up having a poor cooling, especially of the rear cylinder, leading to frequent overheatings that are anedoctally reported to burn out the hairs from the legs of their riders.
Sure the growing presence of the so-called "universal Japanese" or "standard Japanese" motorcycles such as the Honda CB 450 all around the world since the late-'60s ended up relegating American motorcycle makers such as Harley-Davidson and Europeans such as BMW Motorrad to lower-volume niches with a higher profit margin, but it didn't really prevent the Japanese to enter those very same high-end segments with the cost advantage of a full volume production. Nowadays, even in the custom/cruiser segment which is the last one that Harley-Davidson is still present owing basically to its "tradition", there will be some competition such as the Suzuki Intruder series. Apart from technical advantages such as increased performance, efficiency and comfort, the liquid-cooled V-Twin engines offered by Japanese motorcycle makers don't compromise the aesthetics sought after by those who are into the custom motorcycle scene.
Other cylinder layouts, such as the flat-twin featured in the BMW R-series and the parallel-twin which is more frequent in British motorcycles such as the Triumph Bonneville, also have advantages that must be considered. While an opposed-cylinder engine sets the center of gravity a little lower, thus leading to an enhanced stability in crosswind conditions, an inline-cylinder still has more main bearings to support the crankshaft and its loads compared to every other layout. When it comes to cooling, since the most usual setup for flat-twins in motorcycles is a longitudinally-oriented crankshaft with the cylinders hanging out to opposide sides, they get exposed equally to the oncoming airflow much in the same way observed in a transverse parallel-twin.
Even though Harley-Davidson engines are usually set to narrower RPM bands more comparable to a car engine that turn them more suitable to some relaxed cruising, and could actually fare reasonably in a compact car as long as some improvement to the cooling air flow is applied, most of the competition offers a better performance at a broader range of conditions. And then, basically what's left for Harley-Davidson is cater to those more attracted to that "one-percenter" profile.