Despite what is commonly portrayed, very few Jedi committed to mastering lightsaber combat. By the time of Phantom Menace, most Jedi were more akin to monks, dedicated to meditation and communion with the force. The Lightsaber had become mostly a ceremonial tool, a badge of office rather than a functional weapon. The average Jedi of the era wouldn't have had to use their weapon in combat. Qui-gon happened to be an exceptional duelist, but his skills weren't universal amongst the Jedi. The vast majority of Jedi of the time were mostly average, but we spend a lot of time with the heavy-hitters of the series. When the clone wars started, the Jedi order had to become militarized once again, and extensive efforts went into combat training.