What’s the structure of the importing content source? You might still make the pattern you are looking for, but not with just slug.
There are a bunch of values available, listed in the permalinks doc. The way it normally plays out is to create a general pattern to capture as much of a given section as possible, and then override on the individual content piece level by setting front matter to produce the permalink values desired, with title, slug, or url (see the front matter doc), if needed.
Folks have tried a lot of content strategies, so the easiest way is to just point to a site, repo or example online. Then we can recommend.
It is a common practice, and a good one, to keep loose pages in their own section, so for this example that is pages and the /:slug/ means we can create a slug in front matter and “place” a page wherever we want.
Want https://example.org/about-us/contact/? Make a file at /content/pages/contact.md and in front matter set slug = "/about-us/contact/".
As for videos, that is a section, so it can have it’s own pattern. The one I suggested worked for most things, and you can set the slug when a video’s name doesn’t map well to URLs.
Now, the obvious omission is what happens at https://example.org/videos/. I didn’t know what you wanted that page to be. So, the default idea is a section root being a list template, listing the pages beneath it, with access to pagination, and other niceties. You can customize it, of course. You could say, add text or images in a content file, that would have the underscore: _index.html. And if you want that specific page (/videos/) to behave differently you can override in the layout template for that specific section (I’m running out of steam and have a 7 year old to wrestle, so I’ll leave it to you to figure out which template that is).
Whatcha think? Doable with your current content structure? I’m not adverse to debugging your specific site, if you’d like to contribute it as an example to our community on how to migrate an existing Jekyll site.