While one can probably hire an expert to say anything, it's going to be difficult to establish construction defects in a 40 year old building. Missing steel in the concrete might do it but the way the slabs held together makes that look less likely.
I noticed in the Engineers Report, he described the flat pool deck (no slopes to drains) as a “major flaw” in the design. I’m not so sure the code required it. The major flaw was the fact that the leaking went significantly unchecked for years. Very expensive to pull up all of that pool deck to re apply water proofing.
The HOA knew it needed to be done, and they put it off. That doesn’t mean it was the cause of the collapse though. My guess is that a drunk someone came driving into the garage at 1:30 am and found the weakest column to slam into. Unfortunately, the next column over wasn’t much better off.
Here is an apartment building that was built in 1952. I think that it still looks pretty good. I lived there in about 1953, as an 8 or 9 year old. I just happened to remember the address. It will turn 70 years old next year. https://www.apartments.com/22-atlantic-st-se-washington-dc/eg649xm/
I’ve read reports that damaged concrete exposed rebar to salty conditions.