Gate agents can be real pricks. I have witnessed that myself, picking up the paperwork and watching as an agent happily tells some pilot the jumpeat is already taken. I intervened in that case, asked our online pilot to non rev in back and got the offline pilot on the jumpseat, which seemed to piss off the agent. Have to say I enjoyed pissing off that agent.
I would not bet on Delta getting more jumpseat access though. Management is actually asking for the opposite, they want to get rid of the jumpseat for offline pilots, or something to that effect.