That's surely just a case of saving on the costs of modeling, rigging, animating and voicing another leader (especially since all five are linked to 2K and Firaxis trying to sell us something extra on release).
Personally, I'd take half the leaders and twice the personas for 20% more civs - especially in an edition of the game where leaders & civs are unlinked, so it really doesn't matter if I'm playing Ben Franklin or a Professor Machiavelli.
I don't know if I would go half the leaders and twice the personas necessarily. I do like seeing different leaders each game, I would hate if Machiavelli was in every game I played. But I would easily trade like 5 leaders if we got a second persona for everyone else in the game, for example. And certainly where we are now with the game, I still have maybe 5 or 10 leaders/personas that I haven't fully played through yet, so I'm not desperate for more leaders. But would definitely like them to bulk out the civs rosters more in the near term. I really don't think they need packs that give 2 leaders and 4 civs - give me like 1 leader, 1 persona, and 6 civs.