You can avoid this during booking by booking the “direct” flight as two separate segments (sometimes possible using a third party booking site or by using the multi city tool). But once you’re booked on the “direct” flight, in my experience you’re basically stuck. Other passengers on the ATL-DTW flight will be on the upgrade list, etc. and it will be treated as a normal domestic flight for them - only the passengers booked on the full international itinerary as a single “direct” flight are affected.

I agree this is a deceptive practice and that the concept of “direct” one-stop flights is no longer relevant in the modern airline world, given that the airplane isn’t even the same and there is no benefit to the customer to the designation. (In fact, there is negative benefit because you will have seat assignment and upgrade issues, and you only earn mileage for the distance between origin and destination, ignoring the middle connection city.)

Now, if you can somehow get an agent to split the flight into its two component flights, it would be possible to apply an RUC to the domestic leg. It can’t hurt to call and ask - I suspect you’ll be told no, but if you’re successful it should result in all the various problems around the direct flight booking being resolved (including mileage earning).