I get those points, but Fukushima was 10 years ago so clearly it couldn't have been that urgent. Really this has been about reducing carbon emissions. It is clear now that the full impact of natural gas is much larger than originally understood.
The cynic in me knowing that it is owned by PG&E thinks there are a few very expensive maintanence items coming up that the owner has decided it would be more feasible to just shut it down rather than doing the repairs to keep it going. The expense is what led to the decision and not public pressure, but since they won't admit to any of that, the pressure groups claim the victory.
The funny thing is when they finally "won", members of these same groups immediately started bleating about the massive amounts of lost tax revenue that are now looming large over local budgets.
The closure has nothing to do with maintenance. The steam generators still have tons of life in them, the reactors are fine, etc. The main driver is California's renewable policies that would mean the plant likely wouldn't be at 100% every day, which is where it needs to be to stay economically viable.
Fun fact: Diablo's "battery" is the Helms Pumped Storage Facility. It is extremely cool — a perfect Bond supervillain lair.
[edit: typo]