Crisis of Infinite Earths was DC comics saying, in essence, new fans found the multiverse too hard to get their minds around (meaning not smart enough) so they knocked all the Earths down to five and merged them.
But if you follow DC comics they have spent the last 25 years admitting it was a mistake because now we are back to having a multiverses.
The pre-Crisis is what set DC apart from Marvel…and they ruined it. And now we have the Arrowverse prepping their own version of Crisis for fall of 2019
Big mistake 2.0?