I think what makes Katy unique is her out of this world personality. it's super fun, goofy, nutty and refreshing. It's nice to have a pop star who does not take herself so seriously every now and then.
She's super quirky and fun for her age. And she has a great body, especially her baloons, and no other pop girl comes close to her beauty when she's caked up. Katy all caked up >>>>>> any other popstar, even Britney in her prime.
Music-wise she's very smart about who she works with. She's a smart business woman.
She brought fun into pop music again, she's unapologetic lover of fun pop music On the other hand, she has delivered some great emotional songs, TOY, TOTGA, Not like the movies, BTGOG and of course Wide Awake
She's the most down to earth major pop girl, kind and sweet. She has stayed true to herself.
Honestly, nothing much from a musical stand-point. She's just super self-aware, quirky, knows her lane and stays in it, when to go away and when to come back. That's why I like her
Her stability. Her songs are bops but aren't legendary, but they're still successful. She gets decent album sales through her eras and she's consistently near the top of the pop food chain.