I have not seen a single person try and claim that Biden isn't flawed. It's entirely possible to criticize him and still vote for him given the only other possibility. Until we get away from FPTP voting there is only two options for president in the general election. You wont get away from FPTP voting until you can overrule the GOP in Congress. You cannot do that without winning elections.
The people you're arguing with aren't devoted to Biden. He's simply the only way we can keep Trump from retaking office at this moment. He's also done a lot of good things during his term. I'd argue he's been a net benefit to the country given the context.
We absolutely need to primary Biden and everyone like him, that work has to be done but that shit takes work and time. It's a lot easier to do when we can bring more people into the tent. Painting both parties as equally bad and not worthwhile of your vote is literally making it harder to reform the Democratic Party and actually achieve the things progressives are fighting for.
He was stopped last election yet the threat has only grown.
The threat didn’t start with him and it won’t stop with him. The threat will exist as long as living conditions continue to deteriorate and people seek more extreme politicians in the hope of something changing. Doesn’t matter how misplaced their thoughts on what the problems are.