I'm not comparing Lex and the Calculator status-wise, I'm just saying that Lex is always around. It doesn't matter if he's more a DC villain than just a Superman villain, he's still around. I gave the Hush example as well. Sometimes you have villains that are just majorly reoccurring. And the Calculator hasn't been in ever issue. He just showed up in this book. BoP ended a year ago. I think it's more than acceptable to have him show up. Also, he could be the Lex to Barbara's Superman. Why can't they try to elevate him to a higher status? As long as it's interesting, I don't care if he's around a lot. If they mix it up and have other villains around as well, it's fine.
There are many instances of villains being around a lot where I've enjoyed it. The Hood has been a huge part of New Avengers for half of the book's run, and I like it. Then you have the Goa'uld in Stargate SG-1. They were the enemy in about 75% of that's show's run. And Apophis was the main Goa'uld for over half of that. Then the Wraith were THE villains for Atlantis. I just don't have a problem with constantly reoccurring villains.