Exactly, knowing what we know about anthropology, it's extremely unlikely cuneiform was the oldest writing. What's more likely is that other human groups must have invented ways for storing information, but they didn't survive.
Not necessarily. Logically, there must have been a first writing system (even if cuneiform wasn't it), so you can't show cuneiform wasn't the first on the basis of "something must have come before it".
Writing has been independently invented two to four times that we know of in the last five millennia. (Some scholars debate whether cuneiform, Egyptian hieroglyphs, and Chinese writing were all independently invented, with Mesoamerican writing being the other almost indisputably independent invention.) Anatomically modern humans date back at least 200,000 years and probably would be capable of inventing writing long before our known examples.
Why do we not see more writing in the archeological record? Maybe agrarian societies both motivate writing and are required to provide the free time to invent it? Or perhaps it was written on media that's subject to decay? If some society developed writing on tree bark 100,000 years ago, none of that is going to survive and we'd never know.
The Egyptian and the Sumerian culture were very strongly linked with near identical cultic symbols and building plans for temples up until 3100BC. Chinese writing came suddenly over 1000 years later (minus some shamanic symbols), connectable via the Anu seal (which of course is tentative and will be denied by Chinese nationalist)
> The Egyptian and the Sumerian culture were very strongly linked with near identical cultic symbols and building plans for temples up until 3100BC.
There was prehistoric (i.e. pre-writing) trade between Sumer and Egypt. Scholars have argued that the idea of writing based on the rebus principle—but not a specific writing system—may have been communicated one way or another through this trade contact.
Your claim that the cultures were "very strongly linked with near identical cultic symbols and building plans for temples" is a new one for me—and I volunteer at a museum of ancient near eastern archeology. The material culture of pre-Dynastic Egypt and Sumer are rather distinct from each other. And when we do get writing describing their religion, those are also rather distinct from each other.
I'd settle for "earliest known", without an assumption that there was probably an older one.
Much like fossils, the vast majority of human writing is quickly lost to posterity. Paper, bark, and string decompose; clay and rock break; all writing materials can be repurposed for other writing (palimpsets) or other uses (reshaped to wall stones).
Still, given the paucity of known, independently invented writing systems... We may well know of all of them.
