Oh I’ve been around the scene long enough to remember what it was like back before anime studios started adapting manga into anime panel-by-panel as a default. Some of those 90s series in particular had horrible filler (not just filler arcs, randomly-inserted filler scenes, as well as other highly-questionable changes to the source material). It was a huge relief when anime adaptations started becoming way more faithful to the source material in the 00s.

The problem is that when adapting the story from one medium to another, panel-by-panel adaptation means taking pacing that fits the manga format and awkwardly forcing it into the anime format. So when I say that 5 minutes of manga content gets dragged out to 22 minutes of anime content, I’m not referring to filler, I’m speaking to the nature of the manga vs anime media. In other words, a 5-minute manga chapter turns into a 22-minute anime episode once dialogue is spoken, actions are animated, sound effects are given auditory form, etc. (after all, think about how much faster it is to read dialogue vs speak it aloud, and how much quicker it is to flip through a manga’s action scene of a few panels vs watching the scene fully animated). Sure some substance is added through the addition of a soundtrack, visual flare, and such, however as far as plot, character development, theme development, etc go, you end up with less substance per minute of experience… and it takes a lot of soundtrack and visual flare to compensate for that. Some series pull it off, but it takes a lot of effort, skill, and more importantly, budget, for it to be truly successful. And even then, the thing about manga is that the reader gets to control the pace (they can decide whether to read slowly and savor the experience, or speed through it and absorb as much content as possible as quickly as possible), whereas with anime you cannot (unless you start fiddling with playback speed, which is much more effortful and affects the quality of the work dramatically).