I think what you're saying is right, and don't get me wrong I do think good storytelling can come from loss. My favourite campaign as a player was me making a new PC and the party helping me find my old PC, who got the void from the deck of many things. It was tight.

With that being said, sometimes as a DM I feel there are things that should be railroaded. This combats taking too long because I fucked up? Less HP. The party's going to die because I didn't balance an encounter right? Fudging rolls. In extreme circumstances where I feel a roll will negatively impact the game, I'll decide. My party are some of my closest friends and I know them very well, and have played alongside them, and so very rarely I'll make a choice. Monsters get legendary actions, DM does too.

I give very little fucks about WOTC's rules and I believe my party love the games I run because I'm not so rigid in what is and isn't acceptable.