You're comparing different types of players. Of course someone like Onana wins a much higher percentage of duels, because he goes in for way, way less of them, because he is a sitting midfielder, not an aggressive, pressing ball winner.
Ugarte:
Onana:
Of course you're going to have a much higher percentage of challenges won if you only try to tackle 1.7 dribblers per 90 instead of 4.5.
The concern with Ugarte's relatively low duel winning percentage is best put into context by these numbers:
These are the numbers for Kante at Chelsea while he was unquestionably world class and arguably the best ball winner of all time. 43% win rate. Same as Ugarte, playing the same role.