So when the devs had Ulfric tell me to engage the Imperials at my liberty, did it possibly cross their minds that this might involve immersion-killing incidents wherein I try and kill so-called "essential" NPCs?

Just decided to ransack an imperial camp only to find...

...Legate Quentin Cipius, who's flagged as essential.

Given the amount of good things in Skyrim, I'm starting to think that there are tenured, bad devs at Bethesda who have a "right" to have their ideas in the game, because that's seriously the only way this garbage could've made it in.

A minor improvement would be something like in Oblivion, which would indicate non-killable characters.

The Morrowind system was the best - you just get a warning message saying you tempered with your fate etc. etc. your destiny will be differenet bla blabla