1. That's not necessairly accurate.
Keionte Scott struggled in 2024 when Auburn moved him to Boundary Corner. His first 2 seasons he was fantastic in coverage at Nick with coverage grades above 75+. The 24 season they moved him outside & that wasn't his natural position so he had a hard time adjusting. He also had a mid-season high ankle sprain.
Scott had 2 years worth of film of him covering very well at Nickel for Auburn.
2. I watched full games of Thornton from BC, Tim Lewis deliberately called the Defense to keep Thornton out of downfield coverage. He used him as basically a LB playing in the Rover/SS spot. His primary assignment/first read was coming down backside in run support on run plays & on passing downs he was timing the snap to crash the pocket as a Blitzer. He was rarely dropping in shells; whenever he did, he was almost always in the Cloud Hook & Hole Zones. I could literally count on my hands the number of times they had him in Deep 3rd's.
There's a reason why even when you watch his highlights, it's 90% run support.
That's actually a smart thing to do, playing to his strengths & putting him in position to be an effective playmaker despite his limitations.
He can play in the same role in this Defense & be an impactful player.