I don't know much about the sub's definition, i personally always go from itch.io's description of the tag. As for your point of chess, a game with over 1300 different openings and variants, being an uncreative game, is hilarious to me. Wouldn't every game be exactly the same, if you only calculated the best action each turn? Heck, not even your example of Rubik's Cubes works, because there every new game is random - unless you only follow a set of moves to "randomize" it, that is.
A puzzle game has a set of solutions, by definition. Chess is not yet solved as it is very very complex, but simpler puzzle games like tic tac toe are solved (and are therefore uninteresting to replay after playing out the solved state a couple of times). The same could be applied to chess, once a solution will be found with enough computing power, and Rubik’s cube as well there is always a solution to just execute in fastest Time. I am not saying they are not impressive, I am a huge fan and avid player of chess, and I am intrigued by how amazing it is to solve Rubik’s cube, for me they are insane display of calculating and executive abilities, if you consider them also expression of “creativity” in the sense of finding a not so clear path to the solution, I can agree with that, but they are still pathfinding to the best solution on the graph of game states :)