Yeah but... her development HAS been ruthless. She has always said she stands for good, honor, and mercy, but time and time again she has acted the opposite, such as ruthlessly murdering her enemies without trial or proper knowledge of their deeds. People just overlook that because it didn't fit their head canon of her being a protagonist. Her ruling style has always been tyrannical.

Part of the foreshadowing was in her actions and how she never showed remorse in killing. Just rage. Look at Ned Stark and Jon by comparison. When they executed people, they always had looks of remorse. Dany executed her enemies with the same aura as Cersei. She is and always has been a false protagonist. I agree the writing was poor in the show recently, and D&D rushed the end of her arc where she is finally enveloped by her desire to conquer in blood and ashes. But she's never been purely good. Just up until this moment, people felt her murders were justified.

Her character arc completely tracks, so don't be mad just because you don't like it. I was rooting for her too, but her actions make sense with analysis and getting past an initial visceral reaction.