Its slow because it's read by a camera. That takes extra steps, and like you mention, lighting conditions. A QR code has to be detected, read and decoded, and thats after the image is processed. An NFC is orders of magnitude faster. Heck even an old school magnetic strip is faster than a QR code.
A better application for QR codes is scenarios where it doesnt matter that its slower. Airline checkins, concert tickets, etc work well, a busy subway where people are queueing to get through a barrier as quickly as possible is one of the worst places to use it.
When I travel to work, the time from me rotating my phone screen to present it to the qr reader window on the gate until the time that the gate opens is <1 second always. I’ve never encountered a delay, it doesn’t seem all that sensitive to what angle you hold your phone at either, it’s only sensitive to distance I’ve found, you need to hold it no more than 2 inches away.
Separately we have revenue enforcement patrols with handheld scanners. The time from the red flash of the scanner on my screen (triggered by the person holding the scanner, it’s not constantly scanning) until the beep for ticket result is < 200ms, I.e. it feels very much almost instant but with a little perceptible delay.
A better application for QR codes is scenarios where it doesnt matter that its slower. Airline checkins, concert tickets, etc work well, a busy subway where people are queueing to get through a barrier as quickly as possible is one of the worst places to use it.