I am going into the third attempt against these devourers and I can tell that eventually the RNG will swing my way and it will work out, but it doesn't change that this system is nothing but a liability to the game and DOS2 proved that you don't need it. Just my 2 cents so far.
I don't think RPG is bad by itself. For example, I though D:OS1 combat is superior to D:OS2 - white a concept of replacing save rolls with flat armor number is theoretically sound, I felt it hurt D:OS2 - made it's combat rather dull and repetitive.
d20 rolls can be frustrating though, or boring if they are tune too much against or for the player. It's a tricky balance to nail.