Can't say I see a problem.
iPhone 6 plus on iOS 11 took so long to prepare for Apple Pay that the payment terminal would time out before it asked me to do the touch ID.
iPhone X with iOS 12 (either beta) is so damn aggressive, that it usually makes a payment the moment FaceID recognizes me - usually 1 second or less. This is from much further from the terminal than I am used to (iPhone 6+ was typically 1" or touching the terminal, the iPhone X works up to 4-6" away), and I've had it charge the wrong card a couple times because it'll approve the transaction before I have a chance to swap cards after FaceID confirms my ID.