Why meatgrinders are terrible for creating backstory

[Thrudd]

It's the same pattern. You go in: if you die, you are done.
You come out, and you go on an adventure (and through the trauma come out stronger).
The distinction, which I mentioned, is that Raistlin did this alone not as a part of a group.
See Dragon magazine 83, The Test of the Twins.
What happened during that Test - the traumatic thing - had ripple effects on the rest of the stories/adventures.
Yes. As those incremental changes were adopted, it relieved players of having to think about someone other than themselves. (And it also removed that pool of ready to go and narratively valid replacements).

I think my dumb brain misunderstood the sort of "trial" you were talking about, I was imagining Raistlin sitting in court, answering questions, with a possible death penalty hanging over his head. lol I'm assuming, instead, the trial was some form of adventure against dangerous magical traps, etc. (of course). I read the first six Dragonlance books like 28 years ago, but I never had Dragon magazine. I can see how that relates to a "meatgrinder in the backstory".