solarpunk memes

It’s not that the entire system needs to change for this to work, it’s that this working changes the entire system.

Would it really? Capitalism is fundamentally a system of economic social relations, workers sell their labour power to the capitalism and so on - that's the fundamental of it and all the various institutions inside (e.g. the police, financial sector, etc) aren't essential/fundamental to the system. They can be changed/tweaked or abolished when the need arises, but the economic social relation between the two main classes cannot be.

Creating some self-managing community that focuses on eliminating the need for police doesn't fundamentally challenge the system (economic class relations), neither does it really challenge the police as an institution given how they'll still exist outside that community and, as you point out, is able to crush this community anytime if it ever becomes a legitimate threat.

Community self-management would quickly result in the redistribution (and hopeful removal) of the inequalities

The community would still operate under capitalist system which reproduces inequality - after all, the community does need money for things like food, rent, utility, essentials, etc. This requires participation in wage labour/markets which means there's still income inequality, inequality in time one has to participate in the community, some people possibly having extra leverage due to private property ownership or their income/education, therefore new hierarchies spawning as a result, etc.

A commune like that under a capitalist system would be good as a survival strategy where the least well off can be supported and be kept over the poverty line (therefore reducing the need for theft but not eliminating it), but it wouldn't remove economic or social inequality - it will just seep back in from the outside.