*If* the goal is to create two distinct shows with distinct rosters and storylines that, kayfabe, run as two different and possibly competing companies, I think two sets of titles is the only way to go with a hard brand split.

Having one champ on both shows keeps them more unified and creates less tension and generally devalues any potential (inevitable, let's be real) clash between the two brands.

Naturally it all depends on execution and one champ could be positioned in a way that makes sense and creates engaging tension just as easily as two champs could screw the pooch. I do think that all things considered, two champs (two sets of titles really) better positions things toward a more convincing and gratifying illusion of two competing brands.