Basic warehouses do have a capacity of 800 stacks, but your example omits the concept of flow. By this I mean that you've created a "line" where products can move up & down between chests and inserters. A warehouse, however, can flow resources through it in any direction on the 2D plane due to it being a single unit of storage. It also offers a perfectly even distribution of products throughout the space for the same reason.
Then there's the cost of using all of those "intrinsic inserters."
18 inserters = 72 iron plates + 27 copper plates + 40.5 seconds
18 steel chests = 144 steel plates + 9 seconds
1 warehouse = 60 steel plates + 10 iron plates + 25 stone bricks + 10 wooden chests + 0.5 seconds
10 wooden chests = 40 wood + 5 seconds
40 wood = 20 raw wood + 10 seconds
Chests & Inserters: 243 ingredients + 49.5 seconds
Warehouse: 115 ingredients + 15.5 seconds
In conclusion, the warehouse will outshine all complex multi-chest setups because it is far easier to make and far more versatile given enough space. If space is truly limited (and it almost never is in Factorio), then the small size of chests may allow a complex setup to conform to the available space better than a warehouse.
Note that this comparison only takes the basic warehouse into account. The (logistics) storage warehouse blows it out of the water by supplying 2000 stacks in the same area, but is more expensive to make.
