Frank Kogan

I think what's happened is that "counterfactual" has tended to become a shorthand for "counterfactual argument" (or sometimes for "counterfactual history"*): so that it means an argument -- or an exploration of imagined history -- from a premise known (in the world) to be false. So instead of (as per Merriam-Webster) describing the premise, it describes a type of reasoning that posits a premise counter to known fact, to explore (precisely as you do in your post) how multiple causes combine to make something happened. Or what count as causes in history

*eg What would America be like if the South had won the Civil War? <-- this type of counterfactual question generates counterfactual history, either in the form of examination forces and causes (what would be the same and what different?), or in the form of novels. I guess fiction is always counterfactual in both senses!