As for executive actions, yes, the next president can undo them. But the precedents have been established, that the executive can make law, which de facto repeals Article I Section 1 that lauched the American republic.
It is comfortable, yet silly to think that elections alone can cure what ails our country.
I agree with you in the narrow assertion that elections alone can't cure what ails our country, but, like it or not, elections are the method used to select the individuals who exercise the levers of governmental power. Our system is very fragile in the sense that it depends on the people we select, regardless of their political philosophy, voluntarily adhering to the guidelines outlined in the constitution. While there are methods for dispute resolution between branches of government, the only power available to the people is elections. While no voter has more power than another, collectively, we have the ultimate power. As voters, we are all responsible for the government we have, whether it was by our voting for the winning candidates, or by our failure to unite behind an alternative. Winners win and losers make excuses, but either way, elections are important.