Good question friend. It seems to be the most common finding in all the CAI threads. I remember CJ Pony Parts even did a YouTube video a while back showing a dyno pull right before and after a full Cobb intake was installed on their '13 or '14 ST. There was no difference in peak HP or torque, just a slight widening of the curve. If I recall, power came a hair sooner and hung on a bit longer in the 6000+ RPM range, but peak numbers were unchanged. Is there benefit to an intake? Sure, my intake tube did make a difference in throttle response and gave a bit more growl at WOT, which is fun. Will an intake make more power? No, Ford did a decent job here, but it will make the power you have a bit more accessible on the low and high end. Going big turbo, on the other hand, is a different story...
Again, what metric did you use other than a "feeling"? See my problem with Americans is that feelings are too highly regarded though often VERY WRONG.
I will agree that gains over the stock intake tract are minimal, offset by the cost to upgrade. But as the stock exhaust is decent, just a look at the pinched section of pipe right at the exit of the turbo and right into the converter tells you there's a decent restriction in the exhaust system.
The weakness in the stock system are -
a) Not drawing cooler air ahead of the radiator
b) The one size fits all nature of the tube that goes over the valve cover.
Dyno's are not conclusive, but track testing is. The problem with this site is the LACK of track testing, just "feeling", dyno pulls and constant data logging.
Why is an upgraded turbo the only answer when the reality it isn't? If the spool or response of the stock turbo is what is desired then you have another option.... Otherwise there is no free lunch, a larger turbo is going to introduce more lag/mute response; the offset is you make WAY more power beyond 5,000 rpm.