And to further the argument that engineers design our engines to make the most power is also inaccurate. They are designed to meet a bunch of standards, and performance is only part of it.
DING DING DING we have a winner! As a Aerospace Design Engineer, it makes me happy to see somebody point this out. Yes engineering is the application of science, but common day to day reality is engineers are designing to requirements. Ultimate performance of the primary function is only one requirement!
If you don't believe this look at the pictures of the engine bay of the Mazda 6 racecar and the factory diesel for comparison. Both designed by Mazda Engineers, yet wildly different. The race car is designed to the requirements of the race class it is in. The production car is designed for low cost, and as a family sedan QUIETNESS.
When I look for ways to improve my Mazda 6 I'm not assuming the Mazda Engineers are idiots and I'm superior, I looking for places where my compromises are different than their compromises. I'm willing to pay extra and accept much louder volumes from the car than the average buyer would to gain 10 hp.
Said another way, the Mazda Design Engineer was gladly willing to trade an extra 10 hp and maybe even an mpg or 2 with the intake design to ensure that the intake noise wasn't a deal breaker for large swaths of the population and that the cost was on target.
I've looked at the intake from the throttle body out and I think it's entirely reasonable that it is holding back 5% of this car's power. That's my technical opinion of this design as an engineer. Doesn't mean I'm right, but there are independent dyno plots out there for our car that vouch for this that the naysayers have either not seen or are ignoring as somehow bogus.
Despite the air flow restriction of the design of the stock intake, it is still a decently efficient design for meeting the requirements it had to be designed to.
BTW this is not directed at the OP, but the "intake won't improve performance crowd."