That is mostly due to the way they are spread as a less impacted infected person would be more outgoing and spread that virus more. When somebody more impacted

That is mostly due to the way they are spread as a less impacted infected person would be more outgoing and spread that virus more. When somebody more impacted by a virus would be more isolated due to the impact. So the less impacting one gets more exposure and spread. So that in itself would be a factor, however virus can mutate in various ways and it is the mutations that effect the incubation period and that window of being infectious but not showing any symptoms - that is always going to impact things and certainly a large factor in why COVID managed to spread better than expected. But much hindsight and data analysis will play out for years and years, after all - we are still looking at the Spanish flu data and seeing different aspects to this day.