The beats were all there, just rushed. Dany chose fear.
It makes sense since her whole thing has been ruthlessness in pursuit of power. Her impulse has always been Fire and Blood. Earlier she had trusted advisors to temper her impulses, but now they're all either dead or untrustworthy. One of those betrayals was by a dude who has a better claim to throne.
Her goal has always been to rule, to improve her own circumstances: if she can do that while improving the circumstances of the smallfolk that's just a bonus she doesn't really need. She sent a message to all of the Seven Kingdoms.
It should have been like a season of will she/won't she to build the character to the actions, but characterization has taken a backseat to TWISTS.
I went into this season expecting a narratively unsatisfying but visually stunning procession to the end of a story that the storytellers didn't really care to tell and I haven't been disappointed. There was too much sprawl to be condensed but this is probably the only ending to the Westerosi drama we'll ever get.