We've had a literal civil war that left hundreds of thousands dead.
Bland centrism that doesn't appeal to many people won't actually stop the bleeding, either. But either way, you kinda missed the opportunity to explain why Clinton's campaign wasn't the epitome of the thinking you're advocating, or why the 1000+ seats lost by Democrats after 2008 wasn't representative of it, either. It's not like the Democrats were out there forcefully advocating for things like M4A and free college and $15 and getting beat over and over, it was the opposite! Tepid technocratic incrementalism was the flavor of Obama's administration, running away from defending the ACA was common in Congressional races, and they lost state houses across the country. None of this happened because there was a socialist or left-wing insurgency that pushed radical candidates that couldn't win general elections.