MBTs may not yet be obsolete, but the lesson of this conflict seems to be that their utility is massively compromised. They are vulnerable to man-portable rocketry and FPV drones, both of which are cheap and can be fielded en masse. So far no really durable solution to these threats has turned up. Any aspirations of a wider offensive against Eastern Europe must surely be on hold by now. Russia is basically turning physical resources into scrap metal for little return.