It’s frankly an absurd argument. The assumption seems to be that voting a third-party somehow undermines the system. It doesn’t. The electoral college will just ignore your vote and still produce a winner.
It should be obvious the votes in a election don’t affect the rule of that election. Not now, not future. Don’t wait and protest when the election comes; protest year-around for change. Support third-party? Reform primary or local elections. Expand ballot access. Get a third-party into house. Unhappy with the electoral college? Call your representatives/senators to get a constitutional amendment. That’s where changes happen.
This argument is in direct opposition to reality. Nobody was talking about the rigged Democratic Party primary system of having superdelegates until this year, when it appeared they could be a factor. And now? Things are already changing. In other words, the votes in this election already did affect the rule of the election for 2020! You literally could not be more wrong, but that is what happens if you base your arguments on propaganda and speculation rather than logic and evidence. Votes don’t just signal to other voters what is acceptable and achievable; they also drive the conversation and tell the politicians what is not acceptable.
That said, we will see the same with the electoral college. It has not faced a significant challenge in the modern age. It will remain unchallenged until it is brought to light just how anti-democratic it is, how easily it can be used to usurp the will of the people and turn the election process over to the elite. This will not happen by calling your Senator (lol); this will happen when it becomes overtly relevant in a general election, where people realize their will is about to be undermined by the electoral system. The exact same way the superdelegate system was brought to light by an unconventional challenger and is now being dismantled. It only becomes a conversation when people have the courage to vote their preferences and not their fears and the electoral college is put on full display.
I agree that voting is only the tip of the iceberg when it comes to working toward real change but, in a democracy, voting is still a piece of the puzzle. Rhetoric about voting is as well. If I convince just one or two people now or in the future to vote for the candidate they actually like rather than let fear drive them to vote for a candidate they hate less than the worst candidate, then I’ve done far more than I ever could with my one vote.