This "everything happened" approach is a perfectly fine (and fun!) interregnum take on continuity, until things settle down a bit. But eventually, especially for bigger bits of continuity, I think things are going to need to get a little clearer. If you ask a historian in the DCU "When, why, and how did the JLA come together for the first time," the answer should not be "well, because of a fluctuating multiverse, we really don't know."