As far as I'm concerned, a planet that is able to support human civilization ranks just a bit higher on the priority list than a diverse power grid and economic viability.
Is your goal to reduce global temperatures? If so, it needs to be a sustainable effort. You don't get sustainable effort without economic viability.
If your goal is to dramatically reduce temperatures in the next 5 years, why not dump SiO2 in the atmosphere? That would bring the temperature down pretty fast by reflecting out sunlight in the upper atmosphere.
But if your goal is long-term change, we need an approach that works long-term.
Edit: sorry I forgot to mention your point on coal vs natural gas efficiency, I didn't realize it was not that much gain. I still think it's worth it though, since it's still making progress.
How is dumping SiO2 into the atmosphere economically viable? How do you make money doing that? If you're thinking that governments should pay private companies to do it, why can't governments simply pay private companies to produce clean power instead? Without having done any actual research on this topic, I suspect you might find that this would be far more "economically viable" than paying for the experimental climate engineering that might not even work, and might have devastating unintended consequences. For example I imagine shitloads of fine sand in the atmosphere would be a problem for aviation, and that's probably far from the only issue with it.
Large scale battery storage, by the way, is already a mostly solved problem, and possible to do at a cost competitive price.