exactly. Given that the price excludes the inverter, I don't see...

exactly.

Given that the price excludes the inverter, I don't see how Origin's offer reduces the price of Tesla's Powerwall.

Due to capacity fade you would need to buy 3 Powerwalls to have the same warranted capacity as a single ZCell after 5 years. Whilst not all Powerwalls will suffer the worst possible degradation allowed for by the warranty, the fact that it will be unpredictable how long your particular unit will last makes it difficult to provision the right amount of storage upfront. ZCells premise is easy: buy a 10kWh capacity battery, and you get that for the duration of the warranty.