Well you say it's worse than normal, but afaik they're the only ones we've actually seen die. Our experience of shadowlands in-game is fairly limited and we aren't stuck there because gameplay.
But why would they have to take her place? Why should such a pact have to be made? Are you suggesting it's lack of Vrykul descent? If so, why would such a system exist?
"Val'kyr, you can resurrect Vrykul, but if there's a non-vrykul soul there, you can take its place to bring it back if you want to I guess."
What's their motive?