I disagree that killing characters is in and of itself good writing. Like any plot element or trope, the way it's handled determines whether it was good or not, not just the fact that you're killing by itself. It can be done really well and have a deep emotional impact on the players/readers, or it will do nothing but piss people off.
Haurchefant's death was impactful partly because it came out of nowhere, and he was a beloved character who had helped us get this far. But by this point, all of the scions have very nearly or apparently died so many times it won't have as much of an impact, and they've been around long enough that it would just make people angry rather than sad if they were killed. Killing a character just to raise stakes is bad writing. Plus, it gives diminishing returns. The more death that happens in a specific piece of media, the less people will care every time it happens. Especially if it's the Scions, who are always in mortal peril every time. Unfortunately I feel like Game of Thrones' popularity has caused an obsession with character death and created a new generation of edgelords who think that characters need to die for writing to be good.
Then there's the gameplay aspect. I don't think a character that is killed off will appear in the trust for dungeons, at least as a replayable option. Thancred's fight in ShB didn't have as much of an effect on me since I knew he would live since you can replay him in the trust in dungeons over and over. There's also the fact that the Scions represent our character's voice and emotions. WoL is a silent protagonist who has never done too much emoting or great speeches on their own and relies on the characters around them. If we killed ALL of the scions, is the climax of a whole decade of the game's story just supposed to be Zenos/Fandaniel talking to a wall? There's a reason why the Scions came out of nowhere for the fight with Hades.
We already know and were told that Endwalker is the end of most of the characters in the case appearing in future MSQ. But I don't think that will mean a slaughter. Additionally, this is a subscription-based game that requires a happy, paying playerbase to keep afloat. I don't think they'll take too many risks in Endwalker and to think otherwise is naive.
All that said, I wouldn't mind if G'raha bites the dust. /s