Not sure how you can still have this "it doesn't matter" view after the 2016 election. If there was any proof at all that the masses had the power to give away their power, it was given November 10, 2016.
It does matter, but it only matters in small sliver of states, as those states literally can swing elections.
Whether Republicans and Democrats have the same, slightly different, medium different, or wildly divergent views is secondary to the fact that for most Americans, the choice has already been made.
As an example, take Wisconsin - it was a blue state for 8 cycles before swinging to Trump in 2016. Democratic turnout was paltry, in great part because Democrats assumed that Hillary would win without them.