It wasn't about political power. It was about her sense of personal destiny.

She honestly thought, in all the previous seasons, that she was the "rightful" ruler of Westeros. She convinced herself, with her actions in Essos, that she was a savior to the masses. She'd also been told for all her life that the people of Westeros were occupied and that she and her dragons would be "greeted as liberators." (as the old saying goes)

Then she got there and EVERYONE was suspicious of her, EVERYONE just knew her as the scary daughter of the Mad King. She gave up massive portions of her army, the army that viewed her as a god-like figure, to save Westeros from the army of the dead. And the people of Westeros responded with more suspicion, fear, and racist hatred against her true followers. And eventually people within her own ranks were plotting to kill her just like Robert Baratheon had in season 1.

I honestly don't see why anyone doesn't understand this turn. If anything I'm disappointed that the writing was so on the nose. She came right out and said that she thought she could rule by love, but instead all she had was fear. But she thought it was her destiny to rule regardless.

They also spent years telling us that Targaryens are not just keepers of dragons; that they ARE dragons, in a literal sense, that they have dragon's blood running through their veins. With her brother Viserys this was clearly not the case, and that's why she looked down on him with such disdain and scorn when he was killed by his "crown" and she said he was NOT a dragon. Well she IS a dragon, in a much more literal sense. That's why she survived those fires. And they also showed us time and time again in Essos that dragons can't really fit into the world of humans, with those times that Drogon (or whoever it was) scorched people's goats, or worse, children. Dragons kill, because they have the power to kill. And that's what she did in King's Landing.