Shelf B has a failure mode not available to Shelf A; specifically, the joint between the brackets and the shelf is in tension, so it can separate.
On the other hand, if both shelves fail because the brackets pull out of the wall or the shelf breaks then this failure mode is irrelevant.
There are two ways round this failure mode. One solution is to use enough screws from the bracket into the shelf that the construct will support the maximum load that is likely to be applied (that will be difficult if the shelf is chipboard). The other is to have a metal bearer under the shelf and bolt through the shelf into the bracket (with large enough bolts).
In conclusion: There is no fundamental reason that you should not be able to provide a shelf of adequate strength of the design required by SWMBO (and if my experience is anything to go by, any additional hassle will be much less than that involved in changing the design).