Just sticking to DPS from the East Coast, with both JQ and QF operating a 321 XLR daily, each operating with 8 X AKH containers plus bulk hold, JQ 232 seats, QF 190 seats ? I'm not sure whether they have announced a seat count yet. The JQ is going to utilise all of those 8 containers for pax bags, QF would use at least 6 or 7. Each AKH container is equal to about 66% of an AKE used on the 787 and 330, in size, volume and weight carrying ability. The 8 AKH containers are equal to about 5 AKE's. Combined JQ/QF 321XLR's with a total of 16 AKH containers will equal about 11 AKE's in total and they are needed for over 400 passenger bags if the aircraft are full, plus the bulk holds, where are you going to put any paying freight, there just won't be any room. That's the beauty of aircraft like the 787 and 330, carry a full passenger load and still carry 10 plus ton of cargo.
As I said the XLR will be a great passenger carrier, but it can't do full passengers plus meaningful freight, well not unless everyone onboard only has hand carry.
How many bags do you think people take on these flights? Firstly, I'm not convinced QF will use the containers, but I was just making the point regarding the space. Let's assume QF's configuration of 200 pax = 200 bags. The bulk hold can take up to 1.5t of baggage although it's going to be limited by volume (usable is about 5.8 m^3), which will fit about 60 bags. The other 140 will require about 4 AKH containers (or equivalent space). Still 4 available for containers or equivalent space. While JQ will have more seats, they generally load fewer bags.
If we use your math on the bags, then an A319 or A320 cannot carry the bags for normal pax loads. Consider an A319. BA and AF carry between 142 and 144 pax on their A319s and use containerised baggage. The A319 has only 4 AKH positions, which would get you about 140 bags using my math, but only 108 to 126 bags based on yours. What you're missing is the rear bulk space which is the same on the A319, A320 and A321.
I think you've got it a little wrong about the inherent cargo space on the B787 and A330. It varies a lot. Firstly, they're able to carry that cargo because they're operating well within their limits on medium haul. That inflection point also exists, and why Airbus has put so much effort into MTOW increases for the A330. The cargo revenue payload diminishes very quickly as they stretch their legs on longer flights. For example, using the maximum revenue payload on the A330-200 only gets you a little over 4,500nm at ISA (and only 4,000nm on a -300) even though we're seeing QF fly the -200 to LAX probably with little to no cargo. So once you add in some warm temps, the A330s cannot carry its max revenue payload even to some of QF's points in Asia. So even widebodies suffer from these same issues, however, the longer the aircraft the better it gets in terms of its volume, since the marginal cost of adding length to a design is small since many of the elements that eat into volume are fixed volume costs rather than variable (i.e. the A330-300 doesn't take any more space for landing gear and avionics as the A330-200 does). So when you stretch an aircraft (like the A330, B787 or A321) you really do get the yield from the space. The A321 is unique in that it uses some of that space for the fuel, but it's still a large net increase over the A320. The XLR is great in that it actually dramatically reduces that lost space.
Again, I'm not suggesting the XLR is some heroic aircraft, but simply highlighting why an airline might wish to order it over the A321neo to fly routes well within it's range, especially given the limited risk of doing so. Not every airline orders a higher MTOW version for range although many do. The A330-300 is the perfect example, with plenty of airlines ordering the 242t version without putting them on longer routes all the time but simply to get better revenue payload on routes within its existing flight envelop. DL didn't need the 242t for transatlantic range, but enjoys the payload. Think about SQ's A350-900s regionals. Even with the derated MTOW to 250t (similar to what they did on B777-200ERs), it's still intended to allow them to exploit higher maximum structural payloads on shorter routes. The same principle applies to narrowbodies in this regard.