This isn't surprising. It's been pretty clear for a while that initial synaptic graphs are random / arbitrary, and then are later pruned and strengthened / weakened by learning.
As in, the number and type of neurotransmitter receptors embedded in each synapse.
This isn't "disappointing", this was expected. The initial wiring layout is random, though there's some pruning that occurs in early brain development.
This discovery also explains why the brain can withstand damage and indicates that the positions of synapses in all brains of the same species are more similar than different. “Positioning synapses in this way is very robust,” says computational neuroscientist and first author Sean Hill, “We could vary density, position, orientation, and none of that changed the distribution of positions of the synapses.” They went on to discover that the synapses positions are only robust as long as the morphology of each neuron is slightly different from each other, explaining another mystery in the brain – why neurons are not all identical in shape. “It’s the diversity in the morphology of neurons that makes brain circuits of a particular species basically the same and highly robust,” says Hill.
Recently, the Blue Brain Project published a paper arguing that human neurons don't form synapses at locations determined by learning, but just wherever they bump into each other. See video and article here.
For those people hoping to upload their brains by mapping out and virtually duplicating all the synapses—this means that won't work. The synapse locations do not differ from human to human in any useful way. Learning must be encoded in some modulation of each synapse's function.