>>281627184
Get your head out of your ass and stop watching movies and Sunrise OVAs.

Most cel-era anime used flat shading. The vast majority even. That's been the fucking norm since the medium's inception.

Stuff with 3+ tone shading has always been the exception, the mark of a high budget work, and almost ALL anime with 3+ tone shading were slide shows, or, during action scenes, they heavily reduced the shading and coloring.