Rihanna is fine. I mean yes, the Unapologetic drops have been sort of catastrophic, but she got 2 big WW hits out of it including a full-on ballad and she'll probably be nominated for a Grammy or two.
Some artists are here for ~2-year long eras; some are just here for 2 hits and bunch of flops and a semi-successful album yearly. Whatever floats your navy boat?