The fact that we don't have a better solution now is why it's worth researching. We only have modern cars because we didn't consider transportation "solved" when we had horse-pulled carriages. Many people are looking for better solutions right now, because we believe they certainly exist.
Isn’t that true of everything? There may always be something better in the future. It’s ridiculous to say that we can’t have solutions to anything in the present because there may be better options in the future.
No, that is not true of solved problems and solved games in the mathematical sense, which is what we're talking about. E.g. tic-tac-toe is a solved game, no better solution can be devised.
Ok, then please prove that cars are not the solution to transportation. Obviously, you can't, because transportation is not a game with well-defined rules. Detecting the truth is also not a game with well-defined rules. So obviously we're using a different definition of "solved" than the one used in game theory. QED
I can prove that current day cars aren't by opening any car manufacturer's website and seeing the future models...
As to your discussion of well-defined rules, I fail to see the argument you are trying to make. As a reminder we were talking about the game of Go. Does it not have well-defined rules?