How is SARS (2003) different from COVID-19 when the two viruses are so similar?

Question: How is SARS (2003) different from COVID-19 when the two viruses are so similar (SARS COV-1 and SARS COV-2)?

Salient points from the NEJM article published recently:

-Asymptomatic transmission of SARS-CoV-2 is the Achilles’ heel of the Covid-19 pandemic control. ‘Asymptomatic’ means transmission from people with no symptoms.

-Within 8 months, SARS was controlled after SARS-CoV-1 had infected 8100 persons in limited geographic areas. Within 5 months, SARS-CoV-2 has infected more than 2.6 million people and continues to spread rapidly.

-People without symptoms are playing a major role in the transmission of SARS-CoV-2. Why? How? See below.

-A key factor in the transmission of Covid-19 is the high level of SARS-CoV-2 shedding in the upper respiratory tract (nose, throat, mouth) even among presymptomatic patients, which distinguishes it from SARS-CoV-1, where replication occurs mainly in the lower respiratory tract (lungs, airways).

-Shedding means release of viruses from the host cells. Live coronavirus clearly sheds at high concentrations from the nasal cavity even before symptom development.

-These factors also support the case for the general public to use face masks when in crowded outdoor or indoor spaces.