I'm talking about the Ana quest, where V, the antagonist, turns out to be an interceptor that didn't make a contract with Variya, at least if we have to take V's words at face value. This means there are who knows how many interceptors that aren't connected to Variya, the only two we definitely know are are Crescent and MC, so, we can conclude that one big reason why Variya makes interceptors is to protect herself against other interceptors. And I'm not talking about saving Vivian (her sacrifice is necessary, after all), but saving the world where you did save her.
While you do have free will, you will use it to decide to save Amber, to be nice to people, to do side quests, to be angry at Madam X saying you didn't do your job and eventually discover that you can save that world by doing absolutely nothing, to save the rift pokémon, etc. You might have free will on paper, but it only accounts to something if you have enough knowledge to not be lead like a puppet anyway, and that's what Variya counts on. Then you press the world reset button over and over again until you eventually go Renegade, maybe just to know what would happen at that point, and maybe Renegade won't work either, actually it has no chance of creating a good end by itself because fighting for oblivion is fighting for no future, but at that point you have the knowledge of both routes.
In gaming terms, I think you have to play a route, then new game plus into the other route, and new game plus again to get to the true ending. The thing is, from Melia's backwards dialogue, we know that MC "new game plussed" countless time, plus MC has also the power to exchange information with countless other versions of themselves deep inside the Zeight, so it might already be set up for you without you having to manually go trough two new game plusses, so, the ignorant MC that Variya made into an interceptor wouldn't be Paragon MC, but a past version of it.