Centralization is not the problem. Centralization is one of the keys to efficiency. Grocery stores are a centralized solution. Decentralization of the food supply would mean we each grow our own food in our back yards. (Even that is centralization... True decentralization, we would forage for food in the wild, rather than growing it in a dedicated place near our homes)

The problem comes not when we centralized, but when the store owner decided to take a share disproportionate to the value he provides. When the efficiency of his operation saves production costs, but those savings never reach back to workers or consumers.

The next problem comes when he acquires enough power in the marketplace that he can dictate terms without worrying about losing market share.

The solution is to dictate back to him a "level of futility." A level at which any future gains are confiscated, so there is no benefit for squeezing workers and consumers any tighter. A confiscatory top-tier tax bracket was the solution to the Robber Barons of the industrial revolution. Abandoning that control has been an unmitigated disaster.