Can I just say that 80% of music listener/buyers care only about "current pop culture"
that's why Katy Perry, Taylor Swift, Ariana Grande etc have good record sales.

"Female singers" reaching age 30 are "guaranteed flop material" e.g
PINK, Alicia Keys, Kelly Clarkson, Christina Aguilera
But these singers above have huge success in their 20's

While Leona?
Can't remember her exact age but I assume around 25-26 when she released Spirit, and received MASSIVE SUCCESS for less than 2 year.
After ECHO released, #Happy FLOPPED hard, I am so angry they didn't release Outta My Head as lead single.

1. Taylor Swift sucks at singing (vocally) but amazing songwriter
2. Ariana Grande (decent vocal) but good icon for teenagers. She is cute, energetic and refreshing
3. Katy Perry sucks at singing, but released great charted songs
4. Rihanna (bad vocal) but in studio her voice blends amazingly 90% of her songs.

I myself appreciate singers who can also write their own songs. But does it do justice to fame?
I would take decent vocal with great songs chosen any days.

See what happened to Jessie J and Leona Lewis?
Amazing talent but failed to maintain music materials to current pop culture.

Look at Little Mix, they can sing well and PERFORM well.
It's boring to see "diva-ish" singers just standing and singing without good interaction to fans/audience.
Leona lacks the quirks and personality, and she rarely do crazy stuff or at least make people gossip about her.

Taylor Swift being promiscuous / changing BF's?
And yet she sells more albums than the more (vocally) talented singers.

I love Leona so much but sorry to say that she blew her chances, she is over 30 now. Music listener (especially in USA) only care about younger generation musicians. Unless Leona manage to create GREAT tracks with Max Martin, Ryan Tedder, Calvin Harris, or featuring Nicki Minaj / Iggy Azalea.. to make her "current" to pop culture.