The reliability of incarceration data can also vary, but you didn't dismiss that. In fact, all data is unreliable, so should we just give up on comparisons entirely? Unless you have a specific reason to think US/SK numbers are wrong (and by how much - we're not giving up on comparisons over 1-10% errors, when the difference is 10x), what you've done is provided a fully generic counterargument: "well data isn't perfect, therefore I am right and you are wrong."
> Homicides are also a fraction of violent crime, let alone all crime.
Typical feigned intellectual helplessness. Knowing nothing else, if the homicide rate is 2x higher, the most reasonable extrapolation is that violent crime in general is also 2x higher. And we use homicide because it's harder to fudge - if I used crime in general, your complaint would have been over-policing or different definitions instead.
> Also, SK suicide rate
How is suicide relevant to the incarceration rate? Especially when it's legal in both US and SK: https://en.wikipedia.org/wiki/Suicide_legislation