isn't that exactly what it says in the response that you quoted?

You can read for yourself if you wish: https://www.delta.com/us/en/skymiles...llion-upgrades

scroll down to "What to Know About Being on the Waitlist" and specifically the chart in the section "Waitlist Options"

but yes, tldr you "can book Main and use a single GUC for D1" if it helps to hear it again Make sure the agent that creates the waitlist request is aware that you only want to be waitlisted for D1, not PS.