I think you should look at that bag representing dumping on the ground not just the little bag.
I don't think the warehouse inventory space need raising really. Well not if we get more options for storage. It shouldn't be build a warehouse and bang storage problems fixed. That lacks immersion. Crates, barrels and chests need more space. Weapon racks and armour stands need to be working. The various workshops/kitchen need an inventory space that we can craft directly from. Workbenches and alchemy tables also need an inventory in the same way shops do.
Then the warehouse really only needs to fill the role of storing finished goods. For which 600 space really is fine. There is a hole in raw building material storage (eg stone/granite/dirt/ore) not having a specific building. Which is why I suggested a stockpile for those.
new-building-stockpile-t4593/But since they are also map texture. Perhaps it is intended they are stored as piles only in walled off areas.