Not nostalgia. Not every new game in a series develop the old features you like, sometimes abandoing them, or even taking a completely different aproach.
I still like DS1 more for story(lore), world, and enviromental storytelling. I have not played a single soulslike that had the same type of world, where everything is connected to everything.
You are like my friend who has the same stance. For me, all the previous entries are too frustrating. ER is the only one I played through multiple times and I disliked the parts in it the most that reminded me of DS.
I can agree that it is overall the best, but it does not have the best world. I can concede and say atmosphere is better in 3, but saying tunnels is better is wrong. Even if you use backtracking as an argument, you had the same problem in DS3. Also poise and bonfire placement is better in 1.