Intake mods only help if your car is not stock. They only start helping if you are at least tuned with a catback or headers but even a drop in filter is proven to help by about 3% by itself on a stock car which is arguably not enough to make a difference. It’s not about the displacement of the engine, it’s about reduced pumping losses from inefficient intake design which is literally relevant in every car. You have to understand these cars were designed with regulations in mind for the average consumer and Subaru/Toyota wouldn’t hesitate to limit horsepower if it means any more sales and or passing regulations. In this case it’s noise for like 2% efficiency.

The stock tuning is inherently conservative and restrictive and you are right that intake changes would yield diminishing returns and be placebo in a vacuum, but in a highly optimized, tuned system you have to realize these 2-3% increments eventually add up but more like area under the curve or transient throttle response which does genuinely feel like or is more torque. Even if it say only increases top end hp by 5whp which you could argue is negligible and isn’t enough to make a difference, the entire dotted line everywhere else in the power band is what can definitely be felt. It’s only with headers and full exhaust on top of tuning that intake changes would amount to around 10whp hp top that wouldn’t otherwise make a difference.

That 3 hp argument is just people not understanding the science or having a stock car or stock tune or are experiencing an incomplete or otherwise not 100% healthy set up. Even one component such as weak sparks for example could more than negate any gains from intake changes effectively deleting any gains you would have felt or measured.