No one is put into positions of power and influence within the party until they tow the party line.
That's such a defeatist worldview. Did Trump tow the party line when he took it over?
Look, change is hard but not impossible, and there's no better time for progressives to step up than this moment right now, when the Dems are at a historically low approval with the whole country. Everybody hates them for the spineless aristocratic piece of shit fascist collaborators they are.
They gotta go.
Now, whether this means the Dem party dissolves and a new one rises from the ashes, or it gets restructured but keeps the name and all the infrastructure, or it gets bullied into submission by the threat of a third party built by Bernie and AOC — all of that is abstract, procedural, immaterial. What's material is that neoliberals must lose their power to progressives decisively, and the only way that happens is if:
a) people become disillusioned enough with neoliberals,
b) progressives are there for people to transfer their hope/faith onto them.
Both of these are happening to various degrees, especially the first one, but there's still a long way to go for it to be decisive (polls still show Kamala Harris close to AOC in hypothetical presidential bid, but we need an enormous lead like Trump had in the GOP polls in 2022-2023, so the pressure needs to stay on).
Only when enough of the Democratic base becomes completely anti-establishment (populist messaging will get them there as long as they're willing to listen) and demands new leadership, only then will the Pelosis and the Schumers lose their power. They haven't actually feared their base in a long time, and that needs to change now.
So, sure — nobody from the party will put progressives in charge, the party's base of supporters needs to demand it first. Then they can just take the power without having to ask, the same way Trump did in the GOP.