This team is missing basically any toughness. Look at the 99 team that won at KU. Nurse, Horton, Tinsley, Fizer, Rancik, Shirley.
I am late to the thread, and haven't read it all, but this is ABSOLUTELY the answer. Both mental and physical toughness. (Just saw Clone_12 said it too)
Mentally, they still let offense drive defense. If someone misses an open shot (Nader), or thinks they got fouled (Jameel), they all go into pout mode on defense. What's the opposite of spurtability? Collapse-ability? It's been there for a while and seems unlikely to change now. Maybe Prohm needs to go full Bobby Knight on them, idk.
Physically, guys like Kane and Ejim and Houge provided a lot of physical toughness that is totally absent now. Just zero interior defense. Jameel can block shots, but he has no idea how to use his body at all and is usually out of position - he is still very raw as a basketball player. He needs to play meat grinder for an hour a day. And Georges and Nader are both guards trapped in a forwards body.
If you look up TOUGHNESS in the dictionary, there is a picture of Kantrail Horton, chewing gum, sweat glistening on his head, dribbling a basketball, and looking into your eyes like he is going to murder you.