Primaries matter. A lot. Good people actually run in the primary and often don't win just because turnout is so much lower than the general election. It's really the big chance you have to vote for someone you actually like rather than the lesser of two evils.
Yeah, the general election can be pretty pointless if two bad candidates both win the primaries, or even if two good ones win. But still, the state level and congressional races matter a lot too, possibly more than the president because we are seeing what happens when one party controls all three branches and disregards the constitutional checks on the executive branch's power.