We seem to agree: if I tell you the length of two pieces of code but nothing else, you won't be able to tell me which of them is more likely to terminate. It could be the one, or it could be the other. The relationship may not be strictly orthogonal (e.g.: longer code could contain more unintended infinite loops), but enough to call it mostly unrelated.

Same with complexity of rules versus "solving the games". Go compensates for the simplicity of its rules by blowing up the search space (it's a big board), which doesn't take any noteworthy additional complexity. The rules of a Go variant played on a 5 x 5 board would have about the same complexity as if played on a 3^^^3 x 3^^^3 board.

Some of the easiest-to-play children's board games have some of the hardest rules, compared to Go.