Problem with this arc is not even Euphy becoming an empty husk over time. It is once again everyone taking the agency away from Anis and deciding what is best for her while ignoring her. Even brute forcing it against her will.
I said it before i'll say it again. Every shit that happened since the beginning is her shitty parent's fault.
The empty husk thing is extremely overstated, it's a trope that comes up in any and all talks of humans becoming immortal and living for "too long". Even when phased as 'disconnected from how a human should be' that does not change.
Beyond that you just have people with conflicting interests. Anis wants to fulfil her duty (she does
not want to be Queen, that's just what she has to do to fulfill her duty) and atone for pushing it on her brother. Euphy wants to be Queen to prevent Anis from doing something she doesn't want to do just to accomplish a different related thing that she does want to do.
But yes the King and Queen have fucked up immensely for a long time and this whole arc should be just as much of them realizing that as it is anything else.
So basically it's one of those legal contracts where you can get cucked hard if you didn't clearly define the scope of the contract and how big it is early on and with no option to revise the contract in the future, you are damned if you make a mistake.
Yes, you are also possibly damned if you don't take into consideration changing circumstances.
For example if you wished to kill all your enemies, but you ran out of enemies, what would happen? Would you just lose all purpose and will to live or would you broaden the definition of 'enemy' and become a monster that just massacres people.