Naya's Reemergence
Eren's core beliefs remained unchanged even after landing in Labh Salem.
He continued to work hard to sharpen his skills and build a steady foundation.
He kept investing in himself, making full use of the rich and diverse resources available in Labh Salem.
Even though Tantra's practice improved his speed and efficiency, Eren didn't cut down on his efforts. On the contrary, it made him even more steadfast on his Path than ever before.
One could say that what Sansara Sage was attempting to do after achieving Perfect Sainthood was being done by Eren when he was just a Grandmaster Ranker.
He was essentially living multiple lives through the use of his clones, broadening and perfecting his Path even more than before.
All he needed to do at the Ranker's Calamity was to fuse all his experiences and smelt them to achieve Sagehood.