In the UK, Barclaycard introduced an NFC "loop" that fit perfectly on the certain Garmin models about 2 years ago. If this can be done by a bank, I'm not sure why Garmin cannot create a similar "loop" for devices released prior to the Vivoactive 3. Take a look at the link...
Whilst it does not have Garmin Pay and NFC, the Fenix 5 series has a load of features the Vivoactive 3 does not have (The Vivoactive 3 is a solid watch for the right person)
- Power meter support
- Running dynamics
- Training load and status
- 80 plus activity profiles
- mapping and navigation
This is just some of the differences, if people are feeling cheated the Fenix 5 does not have Garmin Pay and feel the Vivoactive is cheating them and cant see the differences then they have bought a watch that is to big for them in terms of features with the Fenix 5