Sure, the change up has movement to it; that alone doesn’t make it a good pitch. In fact according to STF+ on Fangraphs, the change up has been his worst pitch so far in the majors.
Without a fastball to blow by hitters, he’s got to land the off speed and breaking pitches for strikes, and/or fool batters into swinging at them out of the zone.
Again, small sample but in the majors Yoho is not fooling anyone with his pitches. In the majors there has been just an 18% swing rate at Yoho’s pitches outside the zone, compared to 33% in the minors, and the contact rate when a batter swings at any pitch of his is 80%.
So without a fastball and not fooling anyone nor being able to command his arsenal I questioned the basis of your opinion that Yoho has undeniably good stuff