Packet-switching was the invention; ARPANET the implementation. Implementations by committees/teams/groups are commonplace. For you to call it a good counter-example, you need to show that packet-switching was invented by a committee.
I don't think separating the two is reasonable. Was the invention of the internal combustion engine separate from its first construction? Was the invention of the atom bomb separate from the construction and testing of The Gadget?
Conception and implementation are, in my mind, both necessary for invention.
