> The earliest strains of Covid were by far the most severe ones. It's not that surprising to me that the very first patients contracted a strain more likely to put them in the hospital.
No, the only SARS-Cov-2 strain with (likely) decreased mortality is Omicron, see https://en.wikipedia.org/wiki/Variants_of_SARS-CoV-2
The fact that Covid (as an illness) has become milder is due to the hosts adapting, not the virus being milder.
Not only the hosts, but also the hospitals. Treatments became available, and we learned what worked well and what didn't. The care a person who is infected today gets is very different from what people in the first months of the pandemic got and that's improved outcomes.
No, the only SARS-Cov-2 strain with (likely) decreased mortality is Omicron, see https://en.wikipedia.org/wiki/Variants_of_SARS-CoV-2 The fact that Covid (as an illness) has become milder is due to the hosts adapting, not the virus being milder.
> The severity also depends a lot on viral load.
Yes, that is a factor.