Well, if the renewables in question were hydro, I'd say you're wrong, because hydro is fantastic for scaling up and down on demand.

But since we're mostly talking about solar, that doesn't apply. What may apply is that solar will have highest output when it's sunny, whereas in a hot climate, demand will peak when it's sunny — which aren't quite the same thing, but strongly correlated.

That said, you need to be able to handle hot, cloudy days, and for that reason you may be right that you're best off going entirely with one or the other.