Explain what you mean by "cheese" tactics. Explain how mobs stunning you or tripping you or casting spells on you won't also just be called "annoying, not difficult". Explain how it invalidated a large swatch of builds yet somehow the difficulty remains the same.
Obviously, mobs killing you in one shot makes the quest more difficult. At least for some builds, as you said. It's ridiculous to say it doesn't. It's like you are making up your own words here.
Is it the right way to increase difficulty? Maybe not... But it does make the quests harder.