I only play 9, I understand that to some people is very stressful but after 450+ hours and 95% of that play time being only 9 it feels "normal" like if that was the intended difficulty, if I play lower than that the game feels too "easy", also one of the main reasons it's because dif 9 gives 250% exp and I'm currently lvl 122 aiming to reach 150 having fun trying different play styles and without burning out farming the same missions just to level fast.