What they really should have done was just have 2 Robins for it to make sense - Dick who grew to be Nightwing and Damien who replaced him just a few years ago (new DCU time). It's their insistence on keeping Tim and Jason as Robins or even quasi-Red Robins (while pretending Stephanie and Cassandra don't exist- each of them already had non-Batgirl identities and wouldn't have been problematic to shoehorn back in) that's messed up the timeline.

They should have just started over from scratch like they did with Wonder Woman, Superman and Green Arrow. It would have been less problematic.