Well, one also has to remember that, being a d6 based system. Everything in the tabletop is kinda squished into the middle due to there only being 6 results possible.
Basically tabletop isn't necessarily an accurate reflection of "fluff", then again the fluff is extremely nebulous. I guess my method will be if I think something is too weak, add more wounds!
Though a Librarian desperately going all out with his powers to wound/stagger/stun a Daemon prince long enough for his Devastator buddy to rip it apart with bolter fire (possibly while their fellow Battle-Brothers are holding back a horde of lesser daemons) and killing it that quickly is kinda badass, and might be allowed to stand, depending on the circumstance.