Again, the vast majority of people who turn out in primaries are the extremists within the party. The people who voted "uncommitted" are so far left there is no way they will vote for Trump. Might they stay home, sure. They might also vote third party, but they are the extremists, so they will more than likely show up in the general and they will break 90 percent or better for Biden. The same percent of Republican primary voters will McConnel it up too. Primary voters are too tied to party identity to vote against the candidate and too self important to stay home. The election will be decided by those who didn't vote in primaries who are so disillusioned with both parties that they refuse to blindly accept one over the other. If Biden wins, it won't be because more people voted FOR Biden it will because those swing voters voted NOT Trump.
Trump is either loved or hated, Biden doesn't inspire strong feelings in anyone. IMO Biden wins the popular vote by a landslide, 60%-40% or better, but the electoral college makes it a toss up.