It is a strange one. I think there are more factors than fit or not and suspect there is some kind of "marker" that determines severity. I know some fit people who suffered, some very unfit who had it mild. I think it is the same for the vaccines, as people's bodies react differently to the whatever is in it. My wife is still having issues after being vaccinated mid-last year. This is her first bout of covid.
I am not planning on checking out too early - but I am preparing, just in case :)