Weren't Discovery and the Glenn using their spore drives even before the discovery of the Tardigrade? At least they were running tests and making short jumps using it. I don't think Starfleet would assume there would be no other efficient way of using the network without a Tardigrade and just discontinue the use of the spore drive while the network is still operational.
Yeah, but it was pretty clear in the episode that the tests were either dead-ends or extraordinarily dangerous. It was pretty clear that there's no "work around" and that the Tardigrade is the necessary link.