It's funny you should mention scaling, because fusion does not scale like that at all, it scales much better. If you can get a small reactor to work at all, a larger reactor designed with the same principles is significantly more efficient. With fusion, bigger is better.

I do hear what you're saying though. Sometimes there are just simpler solutions. And I actually think you're right, in most use cases solar + batteries is a better solution than a fusion plant. That said, solar + batteries has only become truly economical within the last 5-10 years. At this point there's really nothing "Simple" about photovoltaic or battery technology, lifetimes of study have gone into them. And 25 years ago, solar was cute, it was pie in the sky. And you'd hear these same arguments "shouldn't we be focusing efforts on something we already know works?"