I just don't understand that "ease of sharpening". It just does NOT matter what's on the outside.
The center core is still there and needs to be sharpened and is HARD!
If that center core is easy to sharpen, it is NOT because of the outside. It's because they have tempered it to be so.
Putting two pieces of soft pine on either side of a piece of oak does not make the oak easier to cut through.