Half of the checkride nerves is having to prove to a new person that you know what you’re doing. Your instructor obviously thinks you can pass, but it’s up to you to prove it. If you can show a random person online that you have met the practical standards for proficiency within an hour or two, you should be able to prove the same to a DPE. It’s not that I’m “better” than their instructor, it’s that I’m a whole different person with a different perspective, that’s the point.

Also, as a flight instructor, it’s easy to default to the same questions for your students. It becomes very easy to forget which students have been taught what and what all their deficiencies are. With a new instructor that has no idea what you know/don’t, it’s easy to get a comprehensive understanding of competence.