If you even want proof that letting an outside company QR code or bank cards on transit fare gates is not a good thing, this is it. QR codes are dynamic and rely on all the network pieces working to get the job done: cell tower, app server, internet cloud, etc. When one link fails, things can stop in a hurry. Witness the April 8 QR code transit meltdown in Chengdu China.
Always remember that digital wallets like Apple Pay Suica work without a network connection just like plastic cards. Transactions are processed locally at the gate. And there are Express Cards with power reserve too. It all comes in handy and keeps things moving.