The damage is as you say "more asymmetrical", but it is also closer to the perimeter wall which is also less damaged than the WTC 1 perimeter.
So while the asymmetrical theory has its merit we have to consider that in WTC 2 only a corner area is damaged, damaged in a lesser amount and the damaged area has undamaged structures closer by . Meanwhile in WTC 1 a larger amount of the perimeter is damaged, damaged so further away from any supporting core columns and the core columns are also reported as having suffered greater loss when you add up all the ksi's (5427 vs 5216 for WTC 2 calculated from reported core columns damaged and their ksi rating as shown in
http://wtc.nist.gov/progress_report_june04/appendixe.pdf, page E-14)
Simple arithmetic isn't all there is to it, though; you can't determine the loss of load-bearing ability of a structure by simply subtracting the strength of the failed elements. There's also load path redistribution, which gives rise to imaging effects in which the members directly opposite a severed member will also be unable to carry any load. So, the more asymmetric the damage, the more likely the structure is to collapse.
Here's a simple example. Imagine two horizontal beams, each separately supported by five columns, each capable of supporting slightly over half the weight of the beam. Now, remove two of the beams supporting one column, and three of the beams supporting the other. Does either of them collapse, and if so, which one? The answer is, it depends which of the columns is removed. If, from one beam, you remove the three central columns, leaving two columns at the ends of the beam, each will bear half the weight of the beam, and the structure will not collapse. If, from the othe beam, you remove the left hand two columns, the right hand two will bear virtually no weight at all, and the centre column will bear the entire weight. The centre column will therefore fail, transferring all the weight and a considerable torque to the inside right column; that will fail, transferring all the weight and an even greater torque to the outside right one. So one structure, with barely enough strength to stay up, doesn't collapse, yet the other, with more than 50% reserve, collapses.
I'm not a structural engineer, but I appreciate that structural engineering is vastly more complex than just adding up all the ksi's and seeing if there's a big enough total to make the building stay up. If I'm wrong in that appreciation, no doubt one of the structural engineers on the forum will point it out, then I'll ask him why he's paid so much.
Dave
