Well reading that report, the architectural firm f'd up. They missed specifying sloping the concrete for the sub-base to drain. That would be the one to after. The engineers second because they have to approve the architect's work. The builder.... ahhhh, not so much, they go off the drawings, but that's not to say they won't be in court also. A good law firm might also go after the CAD writer too if they are still in business. 1980 was about the time computer aided design in construction started to gain legs. I'd imagine the architects were using some sort of CAD for a project of this size.If the building was on a soft base then you have to investigate how it was built and then the builder woudl be sued and then the builder would counter to the association for not proper maintenance.
If something extrernal caused weakness in the structure which pancaked then the Master policy will sue the cause of that external incident. BUT what about families that lost loved ones, that is outside building insirance so there will be some class action.
HOWEVER.... imagine a huge group of engineers, lawyers and local politicians fighting over the cause and who is at fauly. This will take a year.
If there is an avenue here going back on these entities, then the condo association messed up in 2018, because that would have been the time to sue for the repairs. The report flat out says they missed sloping the sub-base as per the code at the time.
One things for sure, there's gonna be lots of expert witnesses in these fields called to testify. Ca-ching for them.