I believe you are mixing up cheap with annoying, though you seem to also be suggesting that he is brain dead.
Arakune has the chance to turn the tide with curse and his death combos. Even if he doesn't kill, he has combos which can put you back in curse again. You have to block during curse mode which increases his chances of winning because of the kind of mixup he posesses.
Valkenhayn has amazing (understatement) corner carry and can attain at least 4K of most of his normals in the corner. His 6C is + on block and leads into 5k meterlessly, and he has very good pressure and mixup. Wolf mixup/pressure is also quite obnoxious.
Ragna has more bad MUs than Valkenhayn. Ragna has bad MUs against: Litchi, Mu, Lambda, Jin, Rachel, Relius. Those are just a few and you're forgetting that Ragna does particularly worse against these type of characters with more range because it's difficult to get in. Ragna isn't so brain dead that I could pick him up and win in a tournament. It's more than that, and I hope you can realise this because this is getting redundant.