I think the purpose was getting as much mileage out of Victor Garber before he leaves.
Yeah, but it's getting implausibly coincidental. First, Julius Caesar is displaced to where Mick Rory happens to be. Then, Kuasa is sent to kill someone who has a totem connected to Amaya's. Then a baby Dominator is displaced to Ray Palmer's hometown. And now Mallus and Eleanor Darhk work with Martin Stein's ancestor. That's four out of five anachronisms so far that have happened to overlap with the Legends' lives. Is Mallus doing this on purpose? Is it some side effect of the fact that the Legends caused the anachronisms in the first place by "breaking time?" Or is it just lazy writing?