I feel that 50/50 network partitions/splits are massively overrated as a threat. When has this historically happened, anywhere, and not been resolved soon? What would even be a coherent story by which two parts of the world stay coherent internally but communication between them is not possible? The incentives for maintaining global communication are massive, and there’s no reason why parts of the world that are still capable of maintaining communication internally would not be able to figure something out to talk to each other within a week or two. The thing that’s much more likely, whether in normal life, or due to government censorship, or due to a war, is nodes going offline, either because something happens to their operators or because their operators get cut off from the entire internet.
The inactivity leak is primarily there to deal with this “3/4 of the network goes offline at the same time” risk.