Despite the wobbly state of Apple Pay Suica card UI design in iOS 12.2 and iOS 12.3, real world Express Transit performance continues to improve. NFC performance is a very subjective thing due of all the constantly changing conditions that come into play: device software and antenna design, NFC chip firmware, reader antenna design and firmware, etc. There are also the different ways that Suica calculates transit fare, stored fare (SF) vs. commute plans. No doubt weather conditions come into play too; I swear that Suica response times are slower on torrentially rainy hot days.
Nevertheless, iOS 12.3 beta (16F5148a) Apple Pay Suica Express Transit performance might be the best Apple Pay Suica ever, and extends the solid performance gains and bug fixes of iOS 12.2. I have only tested iOS 12.3 Commuter Suica but, the UI feels equally snappy on JR gates and PASMO gates now, grumpy old UT1-Neo readers are suddenly happy, the iPhone XS/XR dead Suica UI problem appears to be fixed.
We won’t know for sure until the final release, but I hope the iOS 12.3 performance improvements mean that Apple NFC engineers are hard at work going over Express Transit performance with a fine-tooth comb in advance of the Apple Pay Express Transit HOP and Ventra rollouts this summer. It also means that iOS 12.3 is the last major iOS 12 update. If the beta performance gains are delivered in the final release, iOS 12.3 will be a good curtain call for iOS 12.