A single LinkedIn ad rarely needs one video. The feed wants a portrait cut, the square works harder in some placements, stories wants the vertical, and someone always asks for the landscape. That is four exports, each with its own safe zones to respect, and every one of them is a place for the brand to drift.
The traditional route is a production cycle: brief, storyboard, edit, revisions, re-export per ratio. It works, and it is measured in weeks. The newer route is a general-purpose AI video generator, which is fast and will happily compose a layout you never approved, in type you do not use, with copy that spills into the space LinkedIn covers with its own interface.
Neither problem is really about speed. It is that the output is not reproducible. Ask for the same thing twice and you get two different things, so nothing you learn about the creative carries forward.