Some thoughts from my side:
-the discount on the non modular doesn't reflect the difference in the purchase price at all. Ask your dealer for quotes for 2x 3.3 kWh packs or 1x 6.5 kWh and you will be shocked how big the difference is. Whereas the single 6.5 pack is about half a 13 pack, two 3.3 packs come close to a 13 pack. Although you don't have to consider a future repurchase at the first point because you'll have five years of warranty and the pack should last even longer, is still worth to consider
-the modular system has a lot more connectors and is less resistant to the elements, what might lead to more corrosion/electrical contact issues in the future
-when you will be riding in some cold climate conditions as well, riding on a single pack is basically a useless case. Below 10°C air temp, it becomes a fast scooter, topspeed is extremly limited
-taking them out for charging is quite annoying, as the packs are quite heavy and the retaining mechanism isn't very handy. In addition to that you'll need adapters and a separate expensive and bulky charger to be able to perform of board charging. Furthermore you can only charge one after another, to charge both packs at the same time you'll need another separate charger.
I would always buy the non-modular variant in the future. From my point of view, the modular system does only make sense if you want the lower weight for offroad riding in warm climate or for swapping batterys for track use.