Although you could pack the shelf of a pop up for overnights and it will haul meat pretty well, it isn’t a full size pack and the bags are pretty small. It is easy for me to fill up my 28 with just day hunting gear and a layer or two.
The pintler isn’t too much bigger but the frame is a class above. Think compact pick up with a v6 vs full size with a v8.
I love my 28 and it does exactly what I want, which is haul day hunting gear in early to mid season and gives me the ability to haul meat if I get lucky or a stand or something heavy. I switch to my pintler in late season when I am carrying insulation layers just to hav more room in the bag (if mr made a 40 liter pop up bag I would buy it, hint, hint.)
I would never tell you or anyone not to buy another high quality pack if you have the means. However, there is a lot of overlap in terms of capability. The pop up is a smaller bag and it loses points on stability for a heavy load vs the pintler. The real advantage of the pop up is that it is a much more compact day pack, it is lighter and cheaper.