mutations happen not as a response to effective defenses as implied by 'heterogenous immunity', but because the replication process is chaotic, introducing a ra

mutations happen not as a response to effective defenses as implied by 'heterogenous immunity', but because the replication process is chaotic, introducing a range of defects and accidental benefits. it's a random process as likely to prolong as it is to shorten the duration, so has no persuasive power in your direction. as for your second point, we're exposed to coronaviruses of all sorts already (viruses that have spike proteins)--the relevant class of viral disease here--and that's what's likely to have conferred mild/asymptomatic cases in the majority of the infected.