ACE2 is the primary target, because the ACE2 spike protein is “common” to the COVID-19 Genuses. In other words, the common attribute of the viruses is the weakest link that can be exploited. The ACE2 Spike Protein on the variant genuses makes them all vulnerable to the mimicked ACE2 receptor on the NV-CoV-2-R capsule. The ACE2 Spike is the weakest link. I hope this helps you to understand it better.
Dr. Diwan used a very efficient and practical scientific approach by exploiting the virus’ common characteristics.