Certain engine configurations are inherently balanced, others are not. An I4, for example, is not balanced and most designs have balance shafts driven at twice crankshaft speed to quell them. V8s and I6s are perfectly balanced as-is and need nothing else to make them smooth. A 90-degree V-twin (like Ducati's engines) has perfect primary balance, but have a slight secondary imbalance due to the fact the rods are next to each other rather than in the same plane. The 90-degree V-twin is as close to perfect balance that there is, however, in a twin cylinder configuration.
The KTM V-twin, at 75 degrees, is not as smooth as a Ducati. In addition, it's a large twin at 1190cc, so any imbalance is amplified. There is also the fact that twins don't have as many firing pulses per revolution, so, from that standpoint fours will feel smoother to you. I say ride a Ducati and decide for yourself what is acceptable.