This is disappointing, but I remain hopeful that Samsung Pay makes it onto your roadmap at some point…
The main reason I like Samsung Pay is that you can set a default transport card which is separate from the default payment card. No need to launch the app to switch cards. (See screenshot).
Samsung Pay is also better integrated with Samsung devices - such as swiping up from the bottom of the screen (even when the display is off) to access your set favourite cards / loyalty cards. Google Pay cannot accommodate this, period.
As others have mentioned, Google Pay is not available on the Samsung Gear Sport, S2 or S3 smartwatches, while Samsung Pay is.
Supported devices - Samsung Galaxy Note9, S9+, S9, Note8, S8+, S8, S7 edge, S7, S6 edge+, S6 edge, S6, A8, A6, A5 2017, A3 2017
I doubt this will change anything, but at least I can say I tried.
ps: Cornèrcard UK has added support to Samsung Pay today.