Democratic Centralism is the result of communist parties figuring out what works best through practice. It's at the core of the fast response times, stability, and popular support of socialist systems. Each point is developed and proven in importance through practice.

Point 3 is just basic democracy. If a group comes to a vote, what's the point if the minority just refuses to follow? Unity in action is the strength of the working class, it's what turns the sheer numbers into a mighty sword to fight the bourgeoisie, without unity you have a directionless and mushy form. Further, you can have revotes on decisions if necessary down the line.

Point 4 is not as scary as you think. Recall elections are a core aspect of the electoral system in demcent countries and parties if needed. The lower rungs get to elect the higher rungs, the top is only there because they have won elections, and if they lose the trust of the people they can be ousted.

As for factionalism, it's a recipe for instability and this is where capitalism thrives. A competent, unified, democratic body is far superior than competing private interests at achieving the goals of the people. It's part of why China's government, as an example, has over 90% approval rates, while the US as a two-party system has less than 50% approval rates consistently. Having a single party is not anti-democratic, it means everyone is on the same team and is willing to work together.

Overall, I think you need to actually see the success of demcent orgs like PSL vs how a party like the DSA functions. PSL, with fewer party members, gets pound for pound more done. The DSA is highly divided, its biggest strength is its size, but it can't weild it properly. Meanwhile, PSL is growing rapidly, and is at the forefront of the No Kings and pro-Palestinian protest movements in the US.