All viruses get less lethal as time goes on, not stronger, despite all the fear porn that has been indoctrinated into the public over the last year and a half.
But with C19 we are aggressively isolating people with symptoms. This focuses evolutionary selection pressure on the initial infectious stage. In order to be more infectious the virus increases viral load and shedding, causing more serious symptoms; which would be an evolutionary disadvantage, except isolation renders this disadvantage moot.
Also natural immunity general focuses on the nucleus of the virus, vaccine immunity is to the spike. So this forces mutations in different proteins, which has different results.
This isn't true. Given certain assumptions, it's true on average, but those assumptions don't apply in this case.
For a specific example the Spanish Flu hit harder later on.
Wrong. It's generally the case, because a virus that keeps its host walking around will tend to infect more people than a virus that sends them straight to the morgue.
SARS-Cov-2 is unusual in that it's asymptomatic infectious period is really quite long. It's straight-to-morgue capabilities could become much more prevalent with hitting its infectivity too badly.
Smallpox.