Tom,
"if every coordinate system converges on the observer, the observer's perspective is objective."
I see it the other way around. That three dimensional coordinate system is an illusion of objectivity, centered on the observer. Then you add the timeline as the progression of that observer.
Just for a moment, look at it from the outside in, in which you have a volume of a thermodynamic medium, say a pot of water and each molecule of water is an observer. As though it was a crowd of people milling about.
Now each person has a strong sense of equilibrium and objective, so the coordinate system and temporal sequence are instinctive. Yet there is no larger frame, unless you get their attention and point them in a particular direction, ie, if you give them all the same set of coordinates and thinking the same narrative.
Now consider how much belief systems are about defining the territory and attending to a group narrative. Think through all the religions, political movements, company mission statements, family histories, etc. Whether they lead you with hope, or herd you with fear, it's all about getting everyone on the same page.
Then the coordinate system usually converges on the king, or other such focal point.
So, not to convince you, but to try to explain why I don't see the coordinate system as actually objective and why I start thinking thermodynamics, such as where is the heat, the goal, the channeling, the money, the leverage, the feedback, the reaction/blowback, etc.
Regards,
John M