To expand on your second point, if the other side is an unthinkable evil, then the leaders of your side can be as corrupt as they want and betray as many party ideals as they like, because at least they aren't the unthinkable evil. Because in the US you don't get to vote for anyone, you only get to pick who you vote against. Otherwise you are throwing away your vote and letting the unthinkable win. And in the vast majority of voting districts even that doesn't really matter because they aren't swing states.
Ranked voting would solve this issue. I have never read any critique of it that I found convincing. It exists at state and municipal levels. But until the big states switch it won't change the problem. If swing states adopted it, along with proportional allocation of electoral votes (a couple states do this now) it would definitely change strategies for the better.
The effect is that you can't be the most extreme version of your party and ignore moderates in the hope there are more people that hate the other corrupt extremist, because the moderate candidates will get ranked higher than you by both sides of the artificial duopoly.
In that world, the sensational nature of the media works to uncover sneaky extremists so you can rank all the boring candidates higher, or least higher than the extremist you don't secretly agree with. Either way the boring candidates win.
Someone once wrote that the best kings produce the fewest pages in history books.