I have thought about this, about which route is a better default and a setting, but I removed it for some reason I don’t remember right now. I will take a look tomorrow later. I think it was about the unread message indicator. Would you still prefer this route if the consequence was that there would be no indicator for unread messages?
I think the current position is the same as the messages section that was in core.
There is already a great component about changing the order of sections in the sidebar: Navigation (sidebar) menu display control
To avoid conflicts because both components try to override the order it might make sense that admins who want a different order use the existing component (The author confirmed it works using “inbox-section” as the section name).
I’ll have to see whether I can offer an additional setting for this. In any case, I want to avoid the components interfering with each other.