I think it largely depends on if you have your story "planned" and are trying to write it with the entire rough journey already known, or if you are writing as you go.

Manga, especially shounen or long runners, are usually written basically as they are being drawn. So they are basically slowly writing themselves into corners as they progress and often times those corners are extremely bad. They might plan arcs, they might have a short term plan set up, but usually they are literally suffering under the weight of shit they said 3+ years ago that prevents them from doing what they want now.

And yeah. A property means you aren't just writing for yourself. You are beholden to publisher, editor, fan expectations etc.

Because that's another important distinction here, these stories aren't complete when they begin like say a book or a game is. They are subject to the endless whims of reactions and expectations as each chapter drops. And then subject to it again as the anime adapts it.

However, you are absolutely correct in my experience when it comes to writing as a passion/hobby. I've got all the big set pieces and payoffs ready and trying to link them together or get the story started is the struggle.