Office politics or not, you have a problem when people start referring to parts of prod systems as "my code" or "your code". For me, from the point you opened a PR it's the team's code, not your own anymore. Everybody should be able to happily edit this part of the code without even thinking about asking for your permission (though asking for your input would probably a good idea), first to avoid this kind of nonsens…
The underlying problem here wasn't really that someone "owned" that code, but that when someone else did have a useful suggestion to make, politics overrode technical merit. Clearly that had been happening for a long time and resulted in several other potentially useful contributions by others being wasted as well. This seems to be a problem of toxic management culture, not a flaw in the technical processes.