You don't have to be a "literally" great singer, IE have a great voice, to be a great singer. its about music, voice, style all syncing up. Adele's voice would be awful on Video Games, really awful, wrong style, wrong power, wrong feel, just completely wrong. I mean, quite a lot of Del ray's music is, mumbly type, but it absolutely suits most of the songs, and she changes up with a more "clean" singing voice in most of her songs at different points. Adele powering through these songs with a perfect voice, just wouldn't work in the slightest.
Her voice mostly suits her music, its mostly when this isn't true that I don't like the song. If she wrote the music, who knows, very few people seem to anymore, its one of the many things that has turned me off music in general for so long.
As for ridiculously poor live(if she is, I'm saying in general) another thing that has put me off music. The last festival I went to years ago, and the first almost 15 years ago were both so disappointing overall. Muse were outstanding live, Chillipepers threw a tantrum and put in a rubbish set, most of the other stuff was truly disappointing(but you CAN NOT beat Matrix, in a tent at 2am, maybe having smoked something, drunk, when Neo goes "whoa" and everyone laughs together, or the throat bit in the station).
Something just absolutely grates about someone who can't sing but albums can be "made" with any voice they ruddy want. Madonna can't sing live AT ALL, she's a horrifically bad performer(though in her case her music is utter turd anyway).
Basically not having a technically great voice, or being great live makes her.... no different to most musicians out there.