What I meant is that I don't think Civ is a "solvable" system. Chess is, although for the huge majority of humans (or all maybe) it behaves as if it isn't (and that's only 64 "tiles" and 6 different units for 2 sides)... Civ in comparison is a pseudo-open system, with too many variables and possible states (and increasing), that could be easily taken as a permanently open system, therefore unsolvable. If you think about it, it's designed to be unsolvable (that's why it is so addictive).
NNs excel in recognizing patterns; there is no pattern in a good civ game. In that sense, the devs of Civ 6 have succeeded in making it the most open of them all. NNs will not solve a system were there is no pattern.
The pseudo-pattern we have now, in civ 6, is the very bad AI. If they make it just a little more competitive (using all the systems available, for example), the challenge will increase tenfold (it will make the system more open, and weaken the existing pseudo-pattern)... translation: right now, if you do anything wrong, any amount of mistakes, you can count on easily defeating the AI in any war. That is the pseudo-pattern, and it detracts from an overall very good open design that should make the system unsolvable.
EDIT: solvable == an existing meta strategy that ALWAYS works.