How to remove parent from url slug?
If you want to make it the default page that is long, but to get it in the sitemap you could override the sitemap automated job and make it pull the first additional URL slug instead of the default URL (dependant on if a checkbox page attribute is set). I would then use the same code to set a canonical URL meta tag on each page.
This is a bummer since control over URLs is so critical to SEO. It seems to me that URLs should not be completely dependent on navigation and the visual organization of the site. Sure, the default URLs are fine, but the whole path should be customizable. C5's only validations should be to make sure that it is a unique identifier and a valid url.
Also, I find it cumbersome that the alternate paths are automatically reformatted. It would be nice to simply validate those as unique and valid urls since its main purpose is to handle legacy urls.
I guess the other option is to put all pages in the root and have a disorganized sitemap.