> These came through China and are very old names -- tying the seven objects you can see move against the background stars (ignoring Uranus if you know where to look) is an idea going back the the classical era.

Well, the Japanese weekday names come to Japanese through China. They don't originate there; the fact that they occur in the same order as the Western days of the week strongly suggests that they didn't develop independently.

The native (old) Chinese system divides months into three roughly equal 旬 periods; seven-day weeks aren't part of it.