What is bulk video generation actually for?
Three jobs, and they need different batch shapes.
Testing hooks. One idea, one format, ten different first lines. You are not trying to publish ten videos, you are trying to find which of your ten guesses about the audience is right. The 6-second formats are made for this because a bad one costs 10 credits and 40 seconds of your attention.
Feeding a posting schedule. Daily posting fails on the day you do not feel like making a video. Generating a week in one sitting removes that day from the equation. Six videos on Sunday is a week of posts you cannot talk yourself out of.
Running several accounts or products. A catalog of 20 products, three angles each, is 60 videos. Doing that one at a time is a job. Doing it in two runs is an afternoon.
What it is not for: making one perfect video. If you know exactly what you want, generate it singly, watch it, and iterate. Bulk is for when you do not yet know which version is right, which is most of the time.