A PowerWall(tm) is ~13kWh with a 5kW inverter integrated into a box. If you need more storage, you AC-couple multiple together. A battery bank can be many different sizes, and when you need additional storage you DC-couple the batteries together. An external inverter or paralleled bank of inverters provides the AC power for your loads from the common DC bus.
The main advantage of a manufactured assembly is that it is warranteed and supported unit, generally UL-listed, and can be installed by a professional. A DC battery bank generally becomes more of a DIY effort, but the advantage is that it is easier to size both the battery and inverter capacities to meet your specific needs.