If Suica is designated as an express card, then Apple Pay is always active on the watch. It's been that way here for more than two years. I have yet to read or hear of one person who has had money stolen from their by a thief wandering the streets of Japan with an NFC device.
Don‘t be so naive. There is a very good reason that there is a fixed limit (mostly 25-30 €/$/£) for payments with contactless cards without entering a pin - fraud is absolutely real and aleady happening on a pretty broad scale. Here is a report from the UK: https://www.telegraph.co.uk/news/20...card-fraud-overtakes-cheque-scams-first-time/
Is there no limit on pin-less payments with nfc cards in Japan? That would really surprise me.