I had a similar experience on the Magic in January. I wasn't able to look at any deck plans, just given quotes for general categories, quotes which seemed higher than what I'd researched previously, but I had no Internet to check (maybe I was just wrong- who knows?)
It was my first cruise & I didn't know about getting a generic placeholder, & she never volunteered the information, even though I was clearly interested in rebooking, but none of the exact offers she showed me seemed right (& the deposits were high), so I didn't re-book. A placeholder would have been the perfect solution. As it was, it was a lose-lose situation for both
DCL and me.
She wasn't even particularly friendly or enthusiastic, just seemed to be phoning it in. And as in your case, there was no line at all, so it wasn't due to her being pressed for time. Makes no sense for Disney not to train their rebooking CMs better- they could make a shiny penny off of some really good ones.