I told you how the structure failed on 8 March at 10:39am
The angle braces that hold the floor trusses to the core structure are the weakest links - the ones involved in the fire failed. That started the collapse. The weight of the collapsing upper section overwhelmed everything below it, a combination of the falling debris and the undamaged floor slabs tearing away at the fabric of the core structure, explains everything that you see in all the photos and videos of the collapses.
It's that simple.
The core - whatever fantasies you hold for it - is dependent on the floor trusses and external beams, as they are dependent on the core.
What could have withstood the collapse of the surrounding structures? You say that the core had no concrete, it was just steelwork. So that's answered your question then, hasn't it? How could it have stayed up unsupported?
I am coming up against the same problems that others have experienced it. You just aren't listening to anything other than the voices in your head.