I think what is at issue is finding that which is always so, which really is 'self-existent', that is, doesn't rely on anything else for its existence, the one 'true substance'. In the theistic traditions that might be Deity as the eternal ground of existence. I think the Buddhist approach is not to provide such resting place for the conceptual mind - not to provide a 'master concept' in terms of which everything else can be explained. It doesn't deny that there is one, but it does deny that it can be conceived as any particular entity or object of thought.
So is the prevalent conclusion among Buddhists that (Buddha thought that) there IS in fact an eternal ground, but that it's too dangerous for the mind to believe that, so the entire issue is deemed moot? Or that there is no eternal ground? Or that no one can ever know with certainty if there is or isn't?
It sounds a bit like this to me:
There's this guy who's been to the other side of the hill outside his village. He meets with a bunch of villagers who have not been to the other side of the hill. The village, btw, is in dire need of fresh water. They ask him: "Is there a fresh-water lake on the other side of the hill?" Rather than saying yes or no to them, he spends all his time trying to get them to understand why they are asking the question in the first place.