I'm not sure if you mean story sparseness or map sparseness. I struggled with XII and literally had to start over because I completely forgot what was going on in the story after getting sidetracked by hunts and exploring. Similar happened to me with XV but not to the extent that I felt I had to restart from scratch. I mean, I do agree that XII was better fleshed out (regarding thins like what Pauper was saying about Shiva/G...person) but I don't feel that I understood it any better or had it ingrained into my head any better... if that makes sense? xD XII's story was largely forgettable to me, which is a shame as I played through it twice.
Regarding maps, I feel they are also about on par with each other. I feel "far, far beyond" is exaggerated. They're about the same in this area. The main difference would be that in XV, the final chapters really focus you more on the story progression, although you can still technically return to older areas it's something you feel very much removed from at that point.
I agree that hunts felt way cooler in XII. I think it's because they had a good chunk more to them than simple quests for quick rewards with some leveling up. There was a clan, and each hunt had a little story to it (ie, you met the person who was personally invested in the hunt and why, stuff like that).
Also, I can confirm there is 100% DLC stuff coming in to do with what Gladiolus had to get up to during his absence from the party. It's detailed in the Piggyback guide that this is the case. I think there might have been mentions of other DLC in there too but I can't remember off the top of my head and going through the book to find that kind of sidenote is not worth the effort. xD
I'll also note that while the Piggyback guide is awesome as always, it doesn't include a story breakdown like we got for XIII, which is a shame as a lot of the stuff happening in the background could really do with more information, as everyone in this thread seems to agree on.