Good writeup but it overlooks an important detail. The reason “Option C” (Johnson) is perceived as a throw-away vote is because historically, Option C has not received enough votes to be viable. But those numbers are growing, and casting these votes DOES send a message because it’s recorded in the statistics for the next go-around.
The more growth occurs here the more viable these candidates look, and it’s entirely possible one could win if the trend continues. This year we have WSJ, NYTimes, and many other venues reporting on “historic highs” in third-party-candidate interest, particularly in battleground states. A recent WaPo poll found 44% of voters wanted a third-party candidate.
Casting a vote for a third-party candidate is absolutely sending a message. Just because it might not successfully elect that candidate in this cycle doesn’t mean it doesn’t have an impact on future cycles. The writeup above is no more valid for these folks than “Your vote doesn’t matter, this is a blue/red state anyway” is.