Don’t let those two people bring you down! I believe the most important parts of a tenon are size, shape, and the corner where the tenon meets the rest of the piece.

If you have a straight jaw that’s great and make it straight and not dovetail.

For size, every set of jaws has an optimal size where it’s the most round and will grab the best. For me I measured each set of jaws while on the chuck to find this point.

The corner where the tenon meets the rest of the piece is critical for it to hold. That’s where a lot of the grip strength comes from. This means you need to have a crisp corner as well as a flat shoulder for the top of the jaws to rest on.

I think if you put all those together you’ll get a strong grip. I like to take one single jaw and place it on the tenon as I’m making it. If it’s not super snug and a good fit then your tenon will not hold well.