Rofl, what "built-in systems?" I just gave you an example of a SCOTUS ruling which ensures we'll never break free of the extremely flawed two-party system, citizens' united. The entrenchment of the elites is beyond complete by now, we've regressed to unelected authoritarians handing down decrees from on high, like kings or gods. It won't be too long until they drop the facade that is democracy in this country altogether.
You unintentionally hit the nail on the head here, if a candidate wants to win they have to market themselves specifically to corporate interests. Which should never be the case in a properly functioning political system. If Sanders was half the Reaganite that Biden is, the Democratic establishment would've had no problem making him the candidate in either 2016 or 2020. His push for universal healthcare meant he was always going to have the rug pulled out from under him, as the party has far too many healthcare insurance and big pharma sponsors.
The problem is that they bend the knee to fascists and religious extremists in particular who, once in power, are far from toothless. They're also willing to go to any lengths, cheating or resorting to violence, to put those people in power. The Republican party can see the writing on the wall, their last remaining policy platform of "harm the other" is not popular, which is why they're in the process of rejecting democracy wholesale. And as long as Democrats believe they can "compromise" with that viewpoint, they're complacent in allowing the collapse of this nation.
I won't say everything rides on Merrick Garland deciding to prosecute Trump, but I do believe it's a tipping point. Bad enough that the Obama admin didn't go after the war criminals Bush and Cheney to prevent the executive branch being used as a safe haven for criminality in the first place.