“The final design still required a central pylon and cable stays. Construction of the main support/suspension pylon hadn’t even been started.”
I have read that the pylon and cable stays were “aesthetic” and not structural — fake, I guess you could say.
I find that hard to believe. That's a long, heavy span. And, it's got no structural steel in it. All strength is provided by squeezing the concrete via tensioned cables (which apparently they found weren't tensioned enough, which is why they were doing the "test" when it collapsed).
As an analogy, consider a roll of coins. If oriented vertically, they can support a ton or more. If oriented horizontally, they fall apart. However, if you squeeze the coins while you hold them horizontal, they can take some transverse vertical load. That's what was supposed to be going on here.
But, again, looking at the bridge span, there was a rather heavily trussed structure that was going to accept the cable stays, which make sense. But the span platform itself was very thin. That just don't look right to me.