This is why the longer incubation time of this coronavirus is such a concern. It gives a potentially fatal disease more time to spread before it self limits. Also, I've heard reports that some infected are asymptomatic, so it may continue to spread even while taking out some people.
https://evolution.berkeley.edu/evolibrary/news/071201_adenov...
https://www.pnas.org/content/pnas/early/2014/11/26/141333911...
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2639916/pdf/896...
http://hedrick.ucsd.edu/BICD136/PDF-links/Galvani-Epid-evol....
I understand the basics of evolution. I also don’t have any trouble understanding the trades between transmission and virulence. However, this is not the same as saying that the typical virus becomes less virulent over the short term during a major outbreak.