Notice something about these Couerlclaws? They're supposed to be all women, the Couerlclaw King's harem. But in Stormblood, there are male Couerlclaws now.
I wonder what caused the shift in recruiting. Or perhaps SE wasn't paying attention. It is a singular new development that could be relevant to Keepers.
Interesting to say the least.
However; if I recall we do slay him in a level 29 fate.
https://ffxiv.gamerescape.com/wiki/The_Coeurl_King
There very well could be a new Coeurl King then; or at the very least- they've regrouped and someone else is running it.
I don't think the FATE outcomes are established canon. For example, we beat Svara all the time in the Steel Vigil, but she is actually definitively defeated in the MCH chain, in the quest Securing the Locks.
In addition, the Couerlclaw King FATE has been up for a while, but you also get the Moogle Mail quest where he shows up.