So....Rihanna hasn't done anything iconic. She's had memorable moments but nothing she's done has impacted the world.
Mariah Carey CHANGED the game in 1995 by being a "pop" female artist who dared to intertwine Hip-Hop music into mainstream media. Hell, she gave Jay-Z his first #1 hit in 1999 with Heartbreaker. Her move with that made all the suburban teens feel like rap was in which is why so many of them today (descendants of their parents, most likely) are SO much more receptive to Hip-Hop. This is not an opinion, it's a fact.
Mariah also has the best modern Christmas standard, a song that will stand the test of time no matter what success she has with actual studio albums from now on.
Countless artists, including Rihanna cite her as an inspiration. She's SO iconic that every time a female artist (that can really sing) has come out since the 90's, media & public alike scream "the next Mariah Carey" or wow she is inspired by Mariah.
You know what...let Rihanna have iconic, Mariah is LEGENDARY.
The sole reason for Mariah being discredited these days is/was because of Glitter. Yes, she redeemed herself with TEOM. Her breakdown/glitter massively overshadowed the high she just came off of with being the artist of the decade. So unfortunately, a negative situation will always override positivity.
She's well respected but basically, the younger generation doesn't realize it because her last MASSIVE impact was Touch My Body/Obsessed. However, Rihanna has dominated the charts for the past five years.
In short, everyone who's an adult knows Mariah's impact & how important she is. But the kids simply have rarely experienced her. And currently, they're a big joke to her because of the lip-synching & Nicki feud (they side with Nicki).
This doesn't make her less iconic or legendary, she's just not considered "cool" now. The weirdest thing, Adele makes the music that Mariah should be making at her age, but the kids are a lot more receptive to her. So you have to wonder, how much does appealing to the younger generation really work? Maybe everyone just wants relatability more than anything. That's where Rihanna & others win today. Relatable, not iconic.