I don't think this is correct. Your assumption is that the 5 and 6 hitters (Realmuto and Herrera) with Franco hitting 7 will collectively have higher OBP than the 6 and 7 hitters (Herrera and Hernandez) with Franco hitting 8? Or are you positing that Herrera and Hernandez are jointly more effective at clearing out baserunners (e.g., SLG), than Realmuto and Herrera?
I agree that Hernandez would probably be better at turning over the lineup than Franco. But that's at the cost of his seeing fewer baserunners.
I confess I was lukewarm on Franco in the 8-hole. But when you look at it slightly differently... Herrera-Hernandez-Franco could well have been this club's best 1-2-3 hitters about two years ago. What Kapler is doing here is essentially taking that "second division" top of the order, and installing it at the bottom of the order, behind the Phils' new Murderer's Row (McCutchen-Segura-Harper-Hoskins-Realmuto).
And no, I wouldn't swap Herrera and Hernandez, either. If you just wanted to "start over" in the six-hole, you might do that (higher OBP first)...but Herrera plays two roles in the six-hole; he's both the beginning of the "bottom order" OBP to SLG arrangement, and carries enough SLG to help pick up baserunners who aren't driven in by 3-4-5.
I like the lineup. And I especially like that we're debating whether to use our former leadoff man or our former cleanup guy in the 7 and 8 holes, respectively!