If anything, Stampede made me realize how bored I am with typical filler shonen movies, no matter how flashy it looked. And it really feels like audiences want something more substantial these days, when it comes to anime movies.
I agree. I managed to see Strong World again in theaters and it further reconfirmed why that movie did so well. Well enough to get people out to buy 50 volumes of the manga.
Strong World was focused on the iron-clad bond of the Straw Hats, particularly the bond that gets tested it seems like they might lose a member. Strong World also had ambiguous continuity and marketing that made it seem like it was canon at the time.
Chapter 0, Shiki getting name dropped in the manga, the very first time we had a tie-in filler arc….the marketing did an insane job and further blurred the lines between canon and non-canon.
After Z, the initial novelty wore off and I believe audiences wised up to the notion that these movies were never going to have any type of ripple effect or callback in the manga.
I think there's been some sort of evolution in movie development. With One Piece's involvement of Oda in Strong World, Kubo in Jigoku Hen, Kishimoto in Road to Ninja, Toriyama developing the canonical sequel by then in Battle of Gods just as much as Boruto did afterwards and now Kimetsu no Yaiba and Jujutsu Kaisen even adapting canonical manga storyline, there's been a turning point.
I think a 2021 anime movie which just goes for the fillerish lame villain is basically lazy and unappealing. OP staff has to put the most of their efforts to develop a plot which is manga-level. SW did awesome (well, Shiki was Oda's ida by the beginning), Z and Gold also did very good, with Oda developing the characters as he usually do, even tying them to canonical characters and scenery, and Toei putting on some credible plot. While Oda kept well performing into characters even for Bullett, the plot well basically didn't, as there's little to no plot. The whole movie is basically a mash up of a character festival and Broly's first movie, with the villain rampaging until getting defeated. Literally a 1993 plot.
The novelty of all these characters appearing and teaming up in a One Piece movie for the first time was enough to make Stampede the 2nd highest OP movie in Japan and the #1 worldwide. But I do think we need an evolution of the films. A combination of the casual appeal + canon-esque of Strong World and the "Avengers" feel of Stampede, with a plot that puts the camaraderie of the Straw Hats at the center. A movie like that would have the potential of creating another Strong World boom for the manga sales.
Another thing: Both Strong World and Z had "save this portion of the One Piece world" villain goals with Shiki wanting to destroy the East Blue and Zephyr wanting to destroy the New World. While I personally think those kind of escalation threats are ho-hum, this new film might need something similar to that to make the threat feel bigger than just the crew at jeopardy.