Either you didn't read the OP correctly or you didn't understand it. No active runway (I think you mean taxiway?) was involved. The plane was at the gate and two F passengers left.
Though I don't see it as a "complaint" I would definitely write DL to ask about it and perhaps suggest that they consider some option for UG's in such situations in the future. I think they need constructive feedback in such cases.
I rather have Delta focus on real complaints/questions. The upgrades had cleared, the OP didn't get one, the door had closed, it was an exceptional case. Leave it alone, no need for a complaint.