There are also a large number of equally irrational actors waiting to stab the first irrational actor in the back at the first sign of weakness, if not before. Revengeapalooza because you got spanked by the mayflies isn't going to earn you favor in any quarter.
I got two objections here:
1) Yeah, so? A man still gets killed if an idiot kills him in the middle of a street in wrath even if the police arrests the idiot. Not everyone is a rational actor, and surviving the snake pit of the Druuchi does not mean, necessarilly, that you will keep surviving, for it could be luck or a special ability that does not translate to wise decisions, or backstabbing of others or even being a useful compromise idiot.
2) One could argue just as easily that allowing the mayflies to thwack one's nose is what shows true weakness to compariots. One sees, if one looks in history, that these kind of regimes that are based on the will of the strong are full of wasteful and self inflicted harm inducing displays of strength, for no one can appear weak without being devoured. So the need to address the embarassment even with inefficient means so as to not appear an easy target to the other snakes may regardless be the optimal scenario for survival, for appearance of weakness can be more lethal than actual weakness in such a culture.
Although I like your references, what is true for Dread Emperors isn't exactly true for Druchii aristocrats. The later needs to show at least some basic military competence, otherwise their rivals or Malekith will punish them for it. Being good at killing Druchii needs being good at not doing things that would fatally weaken you.
Being incompetent in war is not the fault that brought down most Dread Emperors, it was prioritising emotion over practicality and pattern recognition, a fault the Druchii are just as susceptible to. Heck, the Asur are susceptible to.... scratch that, EVERY FACTION is susceptible to. Apart from maybe the lizardmen, who prioritise instructions.
You can say that a Druchii who invests a lot of resources to a stupid revenge mission because of pride would have been removed? Well, what about a Dawi king that does the same? How can he keep being a king when he acts like that? The impetii favoring vengefulness may be different between the two cultures, but they exist in both, Naggaroth is built on spite.
Heck, just look at Drycha, who has more reasons to be smart than the average Druchi aristocrat, commiting blunder after blunder due to cultural impetii and harming Kislev in the process even though it hurt her more in the end. She only survived that cuz she was immortal.
So yeah, I do believe that being dangerously stupid is a possibility.