The critical part you're missing it that Lana Del Rey isn't complete crap. She's clearly a talented singer & songwriter. She does't perfectly recreate the songs live, but it seems that it should be obvious to anyone that the voice and inflection is entirely her own. I took your advice of pulling up live Youtube videos and she sounds wonderful. She was a wonderfully authentic voice - whether or not it's 100% re-creatable in comparison to the studio recordings is such a ridiculously silly appraisal of whether or not someone is a good musician or singer. You would be tossing aside countless numbers of musicians out the window for no apparent reason if you based their abilities on how well they perfectly reproduce their sound in a live show. Ian Curtis wouldn't be viewed as the quintessentially influential post-punk singer that he is. You would have to dismiss Billie fucking Holiday while you're at it if you have that mentality.
It's as erroneous as judging a hip-hop artist on their ability to "freestyle". It's just such a non-sequitur.
It's also strange how you choose to believe that live performances should be perfectly comparable with studio recordings - while simultaneously claiming this to be because its the performers time to "sing the song their way, not how a producer says they have to play it". How do you begin to suggest that Lana Del Rey not sounding perfectly like the record isn't an example of her "playing it her way" as if she's not an actual musician, but just some sort of industry puppet who's incapable of cobbling together a performance on her own? Particularly when comparing her to Adele. You're comparing them simply on pitch and tone. Forgetting the fact that Adele is a horrendous lyricist in comparison. Forgetting that her songs are far more derivative and anachronistic in comparison to what Lana Del Rey is putting out. It's just silly to compare musicians by the metrics some people to choose to compare them to.