Long time Scrivener user here, and still very happy. Started my PhD thesis in Scrivener just recently, really dig the footnotes and comments on the side instead of inline.
I’ve recently started using the outline mode more to plan larger projects. Thing is that I find it quite hard to work with because the keyboard shortcuts are rather complex. This makes a quick brainstorm difficult i the outline view. It would seem much easier to have the TAB key indent an item (and Shift+TAB to move an item up one level in the hierarchy).
I’ve tried to redefine these keyboard shortcuts in the System Preferences but that’s not possible, it seems (can’t just enter tab as key combination for menu command “Right”).
The thing is, the outliner is really a file view; it’s not a traditional outliner. It’s part of the larger interface rather than an outliner on its own in a separate window, so things like the tab key and suchlike already have meaning and other expected behaviour (moving between interface elements and suchlike). It would also be unintuitive to have the shortcuts in the outliner be completely different to those used for the same actions in the binder and corkboard. All the same, once you get used to them, I personally think the shortcuts work very nicely - ctrl-cmd and the arrow keys will indent, decent, and move things around. And the enter key will create a new item. So you can get things going pretty fast.
If you find the outlining too hard to adjust to during brainstorming, you can use other outliner programs that export to OPML and then import that into Scrivener. It’s mostly a one-way street into Scriv, but if you’re just having trouble using the outliner when ideas are flying around in your brain, you might try a trial version of a program like OmniOutliner, and then try it’s export and Scrivener’s import to see how well they work for you.