Which is correct if you look at the history of how primaries came to be. Parties simply nominating someone is exactly what used to happen. The first Presidential primaries started in 1901, and they still don’t even happen in every state. Plenty still use the caucus system, where a bunch of insiders (usually local people who have volunteered for the party in some capacity) take off a day from work to decide on a candidate. The caucus system has historically been far more susceptible tampering by powerful interests. It literally was a smoke filled room, and is where that metaphor started.

Primaries aren’t some system enshrined in the Constitution or anything. It’s just how both parties have evolved over time. The general population gets its say in the election later on. The system now is far more democratic than the one that existed 200 years ago (with the caveat that we don’t have to stop with progress here).

Obama would never have gotten the nomination in 2008 if the caucus system was still the norm. The leaders of the party wanted Hillary.

That said, I think this approach would work better if there were more than two viable parties. If you don’t like who the Democrats nominated, look the Green Party or Progressives Party or Send Billionaires to Guillotines Party. If they all put a candidate out there selected by party insiders, that’s fine, just vote in the general for whomever you think is the best out of a wide range of options. It’s far harder for corrupt party insiders to game the system in this scenario–for example, it’d be harder to have a place in all parties and setup the candidates you want so you win no matter what. It’s only a problem because we have exactly two parties that matter. Treating multiple parties as private organizations who can nominate whomever they want under any system they want would be fine.