Of course it works after you install the kernel, oneclickroot is just installing the su binary for you since you already did the hard work by installing an insecure kernel.
Oneclickroot works by looking for an exploit, running it, then logging into adb and getting root access. Since adb is already running in root mode, it will proceed.
Try running oneclickroot without the insecure kernel and let me know if that works for rooting it.