You didn't answer my questions. Why do you believe the US is a closed, unchanging, static system? In order for any of your analysis to make any sense, it must be immovable with no trends in metrics, in perpetuity.

Because that's how the spoiler effect works.The more support a leftist third party gets, the easier it is for the Republicans to win.

Not necessarily. Ideas change alongside the ever-changing material conditions.

I can't tell you how to fix it

Evidently.

but I can tell you that an election with 10% Socialists, 40% Dems, and 50% Reps will scare people away from voting Socialists.

Why? Trends change over time.

At least as long as MAGA is a thing

It will be for as long as Capitalism exists, getting worse. Capitalism is declining, and fascism rises when Capitalism is in decay. Only Socialism will fix it, liberalism leads to more fascism. You can't prevent MAGA by voting Dem, you strengthen it.

and the Dems aren't seen as totally corrupt and basically the same as the Reps by the general public

This is increasingly proven to be true, public opinion of both parties is declining.