If you actually believe democrats and republicans are the same then yes, you "win". Voting third party would be the correct choice.
The existence of the phrase "strategic voting" proves a vote is not a blind show of support. A vote in a FPTP system reveals only that you think that candidate is 1. better than the alternatives and 2. meaningfully more likely to win if you vote for them. Adhering to the politicians' lie that a vote means full support isn't logically consistent with how people make choices in the voting booth. Even in ranked choice voting a vote doesn't signal full support, although it would only signal #1 and not #2, which is a meaningful improvement.