Secondly, they've found evidence of two pathogens working in conjunction (however, not necessarily Chlamydia):
SARS a combination of bacteria and virus
China: SARS May Be Linked to Chlamydia-Like Agent
If this were the case, one would have to have a defense against both pathogens. IMO, this is why the virus is more difficult for the body to battle. As far as the case of the super-spreaders, the pathogen that is working in conjunction with the coronavirus may make the combination deadly. However, if a carrier passes the coronavirus to someone without a secondary infection (or one the body can handle), the effects are not fatal.
Maybe in the case of the super-spreader, both viruses were passed, and in the case of the apartment building, an underlying virus was already at work in the building.
If any of this is true, it would mean that two viruses would be active at the same time. Finding a cure for any combination of two viruses would be extremely difficult.
If it's the combination that's deadly, why wouldn't it be enough just to find a cure for one of the two viruses (or, alternatively, find some way to block their synergistic effect)?
By the way, a propos of another comment of yours, I wonder if we should seek out getting colds, to improve our resistance to SARS.