I agree with that. You could say that we leveled up but the problem is that the time between each fights should not be that long thanks to being stuck in a time bubble and as you said we did not have time or training to learn more about their styles. But this expansion was a bit strange anyway. We defeat Titania on our own all alone. The same with Vauthry but somehow for the rest we need the help of all the scions? The powerlevel in this game is really a bit messed up imo and it just feels like its at a level that the plot needs at that time.
I always said that it was not that great to already fight things like Bahamut and other beings like Thordan and his knights that early in the story. (And lets not talk about beating Omega) We should be at a level were only trickery should get us defeated. And yet suddenly we have these two who can beat us. At least they could have made it that we do nearly beat them but then they use unfair methods or truly something we do not know to defeat us at the last moment. This way we would look way better and it makes sense that especially on the first we suddenly are able to mob the floor with him solo.
About the Ranjit himself: I also wonder how much difference in strenght having more soul makes. It sounded like we would become more powerful and Emets words does hint at that too yet Ranjit with only 1/14 of a soul has the same power level than us with 8/14 of the whole soul. He might have had more years but he also only had one continent to train his strenght with since 100 years ago the rest disappeared. We on the other hand not only can in canon job change and learn/master these jobs quite fast but had enemies that should be beyond mortal limits.