It would be great if the Illustrator Preferences had a way to specify a central root folder for the location of (and default save location) for add-ons, such as Brushes, Graphic styles, Swatches Templates, and others. (Similar to the existing "Additional Plug-ins Folder" setting).

Illustrator currently seems to have very scatterbrained way of handling files, which I am sure there is some history or reason for, depending on the team that happened to develop that section of code.

Examples:

If you save Brush, Symbol, Graphic Styles, ..., libraries, when it defaults to want to save under a long winding path, that at least is in a user-area.
Such as "C:\Users\username\AppData\Roaming\Adobe\Adobe Illustrator 25 Settings\en_US\x64\Symbols".
I blame Microsoft for the dumb Appdata location, but the path is in an area no sensible person would ever save anything. Plus, it is on the system/boot drive, where I usually do not save data. And finding the path if you want to put a brush library there is under the "hunt and peck" method.. (Hmm, is it Roaming, Local, or LocalLow I should go to.)

Interestingly enough, if you try opening such libraries (Open [type] Library -> Other library", then suddenly it defaults to a path under the "\Program Files" install area, like "C:\Program Files\Adobe\Adobe Illustrator 2021\Presets\en_US[type of library]" Now a completely different location (where Illustrators own predefined Presets were installed).
As if any added brush/symbol/styles libraries should ever be added there, since Program Files is usually a protected area that requires admin rights to write to.

To be extra funny, if you use "Save as Template" or "New from Template", then magically it defaults to want to save or open templates from an even more goofy path

"C:\Program Files\Adobe\Adobe Illustrator 2021\Cool Extras\en_US\Templates".. ("Cool Extras" my foot. :-) )

Things such as Actions, have no default. Both Load and Save actions dumps you to a default of "This PC", on Windows.

First problem with all these paths are that they are either program version (year) specific, or version specific (like the Appdata "Illustrator Settings 20xx" paths).
Second problem, that some are in user areas, some are in program/system areas.
Third problem, that it makes it very difficult to remember where everything should be put, if you create or buy a new item. Unless you want to keep hunting for Illustrator's preferred location.

So, hence the wish for a way to define a common root-folder Preference setting, where all Illustrator add-ons should be default saved, default opened.

Personally, I currently resort to creating Shortcuts in all these locations, pointing to where I really keep my brushes/swatches/templates/...
Like "Local Templates" and "Local Brushes" shortcuts (symbolic links) that in one extra click can send me where I really keep all my stuff.

Under my personal resource space I then have a root folder for Illustrator (Illustrator-Adds), which has subdirectories for each type. See attached.

One problem with this scheme is, that when a new Illustrator version comes out (year number or major version number), then I have to go through all the locations and create new shortcuts again, since in the Adobe install scheme, suddenly all the default paths (using year or major version number (23, 24, 25) in the path) have magically changed again.