So it took about 3 weeks of non-stop playing to do, but after performing exclusively single rolls and comparing to 2 other people (1 doing all 10X rolls and the other doing a mixture) I have concluded that you are right.
The numbers are all bullshit and the game just throws whatever at you whenever!
Coworker started playing a week back and got 2 Diluc in a row within his first 20 rolls.
The other guy told me he just got 2 Klee in a single 10X roll plus a Noelle.
Meanwhile in my 300 single rolls the only characters I pulled were 4 Noelle/ 2 Sucrose/ 2 Barbara/ 1 Bennett/ 1 Chongyun/ 1 Fischl / 1 Xingqiu/ and 1 Jean.
All other pulls were 3 star crap items or a 4 star weapon.
Conclusion. It's all luck! No math can save you from Paimon's hunger for more dollar bills in her bottomless guts!
Ah, trying to keep my Klees anonymous, eh? I still want that frickin Diluc...
If you are stuck in the spiral of abyss (level 3 room 2)
Just trow all the enemies off the stage, DONT fight them. You are going to waste time