MERS and SARS are not technically influenza. Corona is ACTUALLY another SARS (Severe Acute Respiratory Syndrome) variant. It is actually only the 2nd time that this virus variant has jumped to humans which is why it's so concerning. Nobody knows what it will do.
Whether or not MERS and SARS are flu they were touted as world class scourges and didn’t create the kind of hysteria this one has. Mortality rates for those two are much higher.
My point is ease of transmission may be more important than mortality rate in how many die and how far it spreads.