Edit: I'm very wrong about the terminology here. --- CoV-2 is way more virulent than SARS, as evidenced by the fact it's spread across the entire world. SARS

Edit: I'm very wrong about the terminology here. --- CoV-2 is way more virulent than SARS, as evidenced by the fact it's spread across the entire world. SARS might spread more easily from contact, and it does more damage once it's inside you, but that's only one component of virulence. MERS is also not really comparable - it's very difficult to transmit between humans. I get what you're saying but practical effects just matter more than isolated metrics. Viruses that transmit asymptomatically are more likely to be virulent, because you can't isolate patients. If you're trying to engineer a virus, you want to make it transmit faster than it kills people and you want to make it hard to quarantine.