Thanks everyone for the input. I was just wondering why the kernel was changed but the bootloader staid the same. After reading here, I can safely continue with the updates now
For the record: i can confirm that the fixed updates to the 4.9.57 kernel work as expected on the Raspberry Pi 2 as well as on the Raspberry Pi 3 devices.
$this->bbcode_second_pass_code('', '[ +0.000000] Linux version 4.9.57-2-ARCH (builduser@leming) (gcc version 7.2.0 (GCC) ) #1 SMP Sat Oct 21 17:13:06 UTC 2017 ... [ +0.000000] OF: fdt:Machine model: Raspberry Pi 2 Model B Rev 1.1 ')