However, in terms of influence on hip hop and pop music as a whole, I think Kanye is above Eminem and it's probably not close. Unfortunately, that's a lot harder to measure.
Kanye likes to claim that his music wasn't about gangster rap and that's why he was sidelined for... a couple years... meanwhile, Dre not only made NWA and Snoop Dogg but managed to convince the entire rap world that a poor white kid with drug problems and abuse issues was the next huge thing by doing things that nobody had ever thought to do before.
his influence is waning
The specific claim was "the most popular rapper/hip hop artist of all time". For that claim, I don't see a good reason why the last decade should weigh more heavily than the decades before.