Yeah, I think you nailed it. The advantage or random loot is a varied end-game you can play for a while, which I don’t really care about. The real intended benefit for exploring is finding the tiny green spirit dudes, but I don’t find their benefit to be worth it. I end up just exploring every corner because it’s how I play by default, and then feel a little burned out when it doesn’t feel rewarded at all. It’s a much better feel in a Souls game to go out of your way to fight a hard mini-boss and find a unique weapon, even if it doesn’t fit your build. Whereas in this case, the cool weapon I found may have just as likely popped on the main path.
I like the combat of Nioh a lot more than Souls games which is what draws me through. There’s a lot of depth to explore and a lot of skill to develop, especially as you get more advanced moves through the skill tree. But I think another unfortunate aspect of Nioh is the smaller number of enemy types. Even unique locations can feel repetitive since you’re fighting the same enemy for the 100th time. I think the enemy design is maybe a bit better than the Souls games, so those fights do have more depth and variety, but they still get stale sooner than I’d like.