It doesn't hurt Linux. It hurts a billion Android users floating in a wasteland of devices that never update. But the only part Google could actually control is

It doesn't hurt Linux. It hurts a billion Android users floating in a wasteland of devices that never update. But the only part Google could actually control is if they provided the stable driver interface that the kernel refuses to provide, so it's not like Google is doing anything that the kernel mainlining objective wasn't causing vendors to do anyway in the absence of that stability.