The NextEra graphic says "near-firm", not "firm". Some dispatchable generation is absolutely required.
The estimate is for late 2020s costs, which is not too far away. I'm guessing they ignored the end of the solar subsidy, and all the necessary grid changes to reach 100% renewables.
The O'ahu batteries replace the last coal plant, but not the last fossil fuel plant. Also, it's meant for black-start.
Nobody knows exactly what the last mile will look like yet. The graphic doesn't claim to know either. As a reader, you should not extrapolate those near-term forecasts and anecdotes all the way to the end.