It would mean of course, that there is a fundamental structural design flaw in these type of buildings
Yes, of course, but the likelihood of that is approaching zero.
The important point being that the Alaska Uni has used several possible scenarios, using the latest available structural software to disprove the case of the WTC7 being collapse due to fire.
In addition, it seems, they have also indicated that the collapse has happened across all individual columns within a period of just over a second, to cause the global collapse.
Now, the testimony of the fire-fighters is that they have heard a number of explosions 'boom .. boom .. boom'. The streams of molten steel they observed in the basements, was a clear sign that the temperatures were higher than steel melting point (1500 C) ... whilst the fires within the building were in the region of at most 800 C. Thus it is likely that thermite was being used, probably a military grade nano-thermite (Al/Fe concoction). Speculating, of course, but in the absence of any other evidence, likely.