You're so close.

All you're missing is "and quantity of processing is correlated with being unhealthy, making it a useful metric".

I have no idea what you're trying to say here. What it sounds like you're saying is that it is possible for processing to make a product unhealthy, and unlikely for processing to make a product more healthy.

What other people are saying is that this communicates almost nothing. What it does is allow people who are doing very bizarre things to food to hide among people who are doing pretty well known, well-tested, and ancient things to food. It's literally an argument to ignore the specifics, it's an argument for ignorance.