Actually, I'm speaking from 20 years of modifying cars, the bulk of which were turbocharged and tuned by me.You can't make a blanket statement like this. You're just parroting what you've read and talking out your ass.
Watch your IAT and try with and without the snorkel. My setup works best without the snorkel- I logged IAT and with the snorkel my IAT was up 2° C over no snorkel. The OEM snorkel even at highway speeds channels air right next to the hot radiator. In my setup, I get better air from below where I removed my windshield washer bottle and the snorkel's air interferes with air coming from below.
A snorkel doesn't do any good at low speeds either- no matter what your setup is.