That's just not true in real world situations. Stock for stock the 2 cars have identical 0-60, and the average E.T's are within 2-3 tenths, of course the mustang with over 120 more horsepower is going to have a higher trap at the end of th 1/4 but the E.T is a drivers race. The cars also have similar top speeds, with the STI having an advantage there as well.
I agree from a roll the mustang will have the edge stock for stock. Throw in a few bolt ons on the stock 2015 STI though with a good tune and the Mustang is going to loose a LOT of its advantage. The 2015 mustangs are heavier than the 2011-2014's as well and the STI isnt. But a stage 2 STI vs a stock 2015 GT is a coin toss any day..not the blow out you make it out to be...just ask the OP he pulled the GT he raced fair and square. It's by no means a guarantee that every roll race will be won by the mustang either, the STI is still fast enough especially with a tune that the mustang probably wont win if the driver makes a mistake and won't catch up. That mustang GT got owned because the cars are so close that in real world street scenarios if the driver isnt good he looses. Simple as that.
LOL, tell yourself whatever you need to sleep better at night.
Just so you know a stock STI is nowhere close in straight line. It is close to an 05-10 3 valve stock for stock, but any year 5.0 will freight train one.
The STI is a badass car, it's just dog shit slow from a roll in real world applications. Sorry that's the truth. Maybe it seems fast if you're coming from a 115hp civic or something like that but anyone with any experience around any even semi quick cars knows the STI is an easy target on the highway. Sorry