I believe that on time performance can vary depending on the circumstances. Virgin had an on time performance rate in April of only 79% but in May did much better at 87%. Qantas in both April and May maintained 81%.
So while the statistics show in May you had a better chance of leaving on time with Virgin, Murphy's Law would of ensured that you were on the 13% of flights that didn't leave on time for changing airlines!!!
Oh and what was your delay for? I'm surprised it hasn't made the news yet!!