I'm sorry, but I don't see this as an accurate statement. Try this: In a new document, update the Heading 1 style to have a LEFT, leader tab at 2.5. Then apply the legal numbering scheme (Article/Section) - you will see your insertion point at the 2.5 setting with the leader in front of it. Since there is no option in the "Multilevel List" dialog box for leader tabs, you wouldn't even be able to accomplish this using that dialog. And we use this all the time.

So, clearly the setting can be made in the style and the result is the same.

However, if there are technical reasons why this approach causes a problem, then I'd appreciate an explanation as opposed to a declaration.

I didn't mention anything about a TOC, and don't have any issues with that.