And of course that doesn’t take into account films that need to add special effects, many extra steps were required to get the effects onto the film which could use several multiples of film stock for each special effect scene; therefore giving a huge incentive to switch to digital editing and effects. There were several methods like directly drawing on each frame film which was very painstaking work – this was common before digital effects became common.

What you descibed for editing films is not actually what was done. It was done like that for TV, although they were usually already shot on video for that to happen, this is why lots of TV Show from 1990s and 2000s are still in SD Letterbox format. Editing a movie would require you to actually cut and splice the film. They had purpose-made equipment to cut the film and used a magnifying glass and a light table to see the small film frames to get the exact place needed to cut the film rolls. It was a very labor-intensive process so you can see why many editors, especially those in the time-constrained world of TV, went to non-linear editing on computers.