Playable origin characters are cool but when you create a custom one you miss out some of the lore of the game.
Dos 2 spoilers ahead.
For example if you pick a custom made female elf but not sebille herself, you will miss the lore of scions and how Sebille was one before. Also sebille gets a separate special ending as well as fane in DoS 2 but not customs with same race and gender.
As a custom character it would be cool to have a story as well, that you can select the background of and throughout the game you get some special things only for that specific background to that custom character. Sure we wont get geralt of rivia from a custom character but in your head your character could be geralt of rivia.
However, I am actually totally cool with other characters dying that you didnt select simply because of combat mechanics. People can bench gale the wizard at early levels when he is weak then use him when he gets strong. I dont like that to be honest. People should put effort into their companions, even if they survive they shouldn't Level up with others imo.
Why should I care what people do right ? You can say the same about camping in game but it bothers people because why shouldn't you play optimally ?