VESA Adaptive-Sync goes back to the eDP stardard, 2009. AMD simply took that and said “Hey why aren’t we doing that over external DisplayPort”. And they did.
So instead of over-engineering a solution that nobody asked for to create vendor lock-in nobody (but fanboys with Stockholm Syndrome) want they exposed functionality that many many panels already had, anyway, because manufactures don’t use completely different control circuitry for laptop (eDP) and stand-alone monitors.
And, no, nvidia’s tech is not superior. From what I gather they have stricter certification requirements but that’s it.