Both, and here's how you can tell.
Tune the car, keep the factory intake on, and then run it.
Take the factory intake off, put the BBK on, and run it again.
The only way to gain real power with an intake is the bigger MAF, and the
tune to adjust AIR:FUEL for it. I am running the K&N FIPK intake tune,
with the factory intake with a Spectre filter, and it runs fine. As soon
as I can get another intake, I will swap it and see if there are any gains.
The engine is only capable of a max CFM, and the factory intake is well above
the CFM the engine can pull naturally aspirated. The restrictions and turbulence
interference is at the factory intake tube and paper filter. The smooth mandrel
bends of an aftermarket intake remove the turbulence and restriction. Those
accordion sections in an intake tube cause the turbulence. The factory air filter
can be the restriction on air flow, especially as it fills with debris and dirt. Cone
filters, if you were to cut one down the center and roll it out straight, will be twice
as long as the factory filter. The CONE filter covers more area than a flat panel
filter does. A bigger intake tube will increase volume, and if done right, add
a Venturi effect to air-flow as it narrows down to the TB.
Intake does make more of a difference on forced air induction. I had a '15 Jetta
TSI. I put a boost module on it, +4 boost, and ran the factory intake. Was a
lot better, like a whole new car. Then I put the InJen intake on it, and WOW,
what a difference; new car again. Then I went to +6 boost, damn nice. So,
I put the factory intake back on for a test, with +6 boost, and it ran like the
+4 setting with the InJen on. So, they do make a difference for air flow and
volume.