Agreed, we would need an interventional experiment run over years.

Still I offer two ancedotal pieces of evidence in favor of its causal status:

One, when you hear couples fight with a good ratio the tension feels lower in the room, and it seems those positive remarks tend to pull the energy down away from uncontrolled escalation -- how can I really totally go off on you, if you are also making many conciliatory comments?

Two, for several years before marriage my wife and I had a modestly bad escalation pattern. Exposure to other couples lead us to a "hey WE don't want to be that way" realization. With good prompting from each other, we learned when we were doing it, and to NOT do it.

You can argue that something in us, allowed us to do that prompting. Perhaps so, but still an intermediate causal step was the fixing of our good/bad ratio. I feel if we had not achieved that good balance we would not have succeeded. (That said, I think we also learned to expect and demand constructive fighting too, its not just the ratio itself.)

But overall I feel explicitly striving to adjust that ratio is a reasonably good proxy for those deeper changes that are needed.

(Still, I agree we would need a very-challenging-to-perform experiment to prove all of this!)