Extradition treaties work in more than just the direction of the US, and serve a functional purpose, for the same reason that foreign nationals who commit crimes in a jurisdiction CAN be adjudicated in that jurisdiction AND/or in their home jurisdiction.
When I was at Uni, the previous extradition agreement between the US and UK was lopsided but still the UK was able to get US citizens extradited under sufficient evidence. As far as I know, when the agreement was re-negotiated in the early 2000s little changed, and looks like there is at least some evidence (at least from the 2003-2012 period) to confirm this from the UK home office: https://www.whatdotheyknow.com/request/details_of_numbers_of...
As far as the Sacoolas case, I didn't realize I was on the hook for sending her back to the UK to spend some time in the dock.
It always depends on several factors, including how much of a trade relationship runs between the two, or regional defence agreements (among other things).
And while IANAL, I suspect given the relationships we have, the Bahamas almost certainly would, Turkey would be contingent, and Spain would likely be the most resistant for non-economic (capital crimes) as EU states tend to be, but for economic ones...almost certainly extradite someone back to US remand (as has happened before).
