How much dd the Si spin?
I hate how people only compare E.T. and 60' time, but forget about the MPH.
For example, a stock STi (with a good driver) will run low 13's with a trap speed around 101 or 102 mph (I ran a 13.48 @ 101.84 in mine old STi with a decent launch - friend ran a 13.1 @ unknown mph in his '05 with a 1.699 60' bone stock).
Now, lets's do a little comparison. Let's say an STi runs a 13.30 @ 101.5 and a GTO runs a 13.30 @ 108.5. Sure, they ran identical times, but the trap speed of the GTO was much higher. The GTO is, in fact, a faster vehicle, it just cannot launch as well as an AWD vehicle. A typical 'street encounter' from a roll will reinforce this fact - the GTO should take the STi every time, not taking into account normal variables (wind resistance, traction, mis-shifting, etc).
Judging by the Si's times you posted, gti mkv, I'll bet the Si spun widly for quite a distance. If not, then something else is very wrong.
Remember, a low E.T. and high trap speed = a fast vehicle that can launch well. Low E.T. and low trap speed = a vehicle that isn't so fast but can launch well. High E.T. and high trap speed = a fast vehicle that can't launch well. High E.T. and low trap speed = a slow vehicle that can't launch well.
I know there are variables and differences, but this is just to illustrate that fact that the Si was either broken, has really crappy gasoline, was weighted down, or had a VERY crappy driver!