> the recent outages caused by the leap second were due to programming languages (most notably Go) not offering APIs to work with time separately from system time
You are misguided to blame languages or standard libraries for leap second outages: at worst they are to blame for not educating programmers about nonmonotonicity of system time on certain operating systems, depending on configuration and behaviour of their time synchronization client, if available and enabled. Support for various monotonic clocks (each good for some but not all uses of monotonic time) is not consistent across operating systems, and almost no standard library expose any of them, as they should not before third party libraries with this functionality gain widespread use.