>>9041423 [Q]

There is more to this than just a shared binding site on the target cell. SARS-CoV-2 prefers a motif slightly different that SARS-CoV. I believe this is due to a 5 amino acid difference between Cov and Cov-2 S proteins. Engineered gain-of-function? Early reports claimed that difference was proof Cov-2 was not engineered because nobody would have thought to go that route. Fishy.

>>9041423 [Q]

I don't follow the logic. If the S binding protein is altered for a different motif on the cell receptor, it still could have the same binding affinity as the original S protein to the original motif on the binding receptor. Affinity is simply a measure of how well the two proteins fit together.