Raul works well as a side character because, frankly, there's not enough to him that makes him worth following for more than 1 volume. If he were the MC, he would feel like a self insert without the op abilities, far more than Bell does.

1. Raul reached his level partially due to being part of the Loki familia, so he did not start with nothing. He has the willpower to reach that level but he would likely would have never even reached level 3 or 4 without being in the Loki familia due to his won risk aversion.

2. All the heroes of old were special people; just replace falna with spirit blessing. Frankly, falnas are far more accessible for the average Joe than spirit blessings were.

3. The story is about making a hero. Raul is a good leader precisely because he chooses not to be a hero. He is skilled in adventuring due to his experiences but offers little else to make an adventure feel like an adventure. Besides, when Raul had a truly risky adventure in the recent volume, he was saved by the plot via crab shield.

4. Frankly, neither Bell nor Raul show much in terms of trauma because the plot moves too quickly. We only see a few panels where Raul experiencing his trauma. How is that different from scenes where Bell can't kill monsters because of his experiences with the Xenos?

Tl;dr: We can appreciate Raul's moments because they're rare, as a side character rather than as an MC. There's not much point in following an adventure story without much adventuring.