So I understand why "current last name" is important in recent western culture: Mary Smith marries Jones and from then only all documents refer to Mary Jones; then Jones dies, she remarries and she becomes only known as Mary Brown. The computer needs to be able to find Mary Smith, Mary Jones and Mary Brown and know they are the same person.
And I understand why FitzRoy is a good LNAB to assign Isabel, though like most persons of her era, she probably was never addressed with a surname in her life. But the computer needs a LNAB, so we provide one that is as reasonable as any -- and it helps us identify her, too. There were many Isabels in her day. So she marries Richard, son of Yves. Did that do anything to how she was known in her day?
CLN is certainly a useful thing to track for 20th century women and even many 21st century women, because we know women in our era often (but not always) change their names upon marriage. But since we know that women in Isabel's era didn't use last names at all, why must we now assign her a second last name she didn't use, in addition to the earlier last name that she didn't actually use?
Since the CLN isn't for her convenience, it presumably is for ours. I think that's what I'm really trying to dig out here -- what makes it more convenient for us to show her --either under CLN or Other Last Name, with a surname of FitzIves? Because the profile currently shows a CLN of FitzIves, you'll notice that in the link at the top of this query, she is shown as Isabel FitzIves. That is no convenience whatsoever to me, who knows her as Isabel FitzRoy! And since I know she married Richard FitzIves, when I see her listed as Isabel FitzIves my first thought is "OMG, did he marry his sister?" So if what is now up for discussion is who benefits from this convenience, I hope those living genealogists who find it a convenience to see her name written as Isabel FitzIves will stand up and be counted!
This does prompt a request to the WikiTree programmers, however -- I pray that piece by piece the code which completely eliminates a woman's LNAB when presenting a woman's name will be rewritten to always include it at least in parenthesis. If the display above showed her names as Isabel (FitzRoy) FitzIves, I'd at least have a clue who we're talking about!