Sometimes, it seems like they forget about the spore drive. They could have leapt to the other side of the galaxy the instant the away team beamed back from the Archive. The Breen might have the ability to destroy the Archive, but with Discovery gone, it wouldn't gain them anything and how ever long it took them would be time lost for chasing Discovery. When the Breen catch up, Discovery could just jump to the other other side of the galaxy.
Also, why didn't Discovery prepare a fake clue? With 31st century replication, it couldn't have taken more than seconds to prepare a reasonable facsimile of the original. Moll did no more than a visual inspection of the artifact to affirm its authenticity and she had never seen the completed object, only some of the pieces. The real artifact is a small obelisk with a button on top. So, make a small obelisk with a button on top that projects coordinates to a random star system. There would be no way for the Breen to discover the deception except to go there and find nothing.