You must clarify that. You are on a technical forum and that simply is not acceptable. "Mainline" is 4.16-rc2, there is only one mainline, so you are saying it's shipping with an rc quality kernel that is still in active development?
Or do you mean it comes with an LTS? "Yocto and Debian". Debian does not use mainline kernel, in fact, no linux distro does, ever. What version of debian?