Longevity yeah, obviously there's no comparison, and likely never will be as you don't get rap albums from people in their 70s. And for that reason you could put Bowie over Kanye, but it was the "several leagues apart" that I disagreed with more. It just doesn't seem fair to say someone can't be put above (or even close to) Bowie until they've had that sort of longevity, no matter how good they've been.
Quality over quantity, and a full 50% of Kanye's albums are considered among the best in his genre, with all the others also very highly rated. See
here, even his worst album has got 9/10s and 5 stars. You can't say the same for Bowie, in fact several of his albums are considered quite bad (Never Let Me Down, Tonight, Hours and more).
Not that the charts are a brilliant way of recognising the best music, but 13 weeks at the top in 50 years is pretty terrible. Kanye got 10 weeks from one song.
Wrt Snoop and Dre, I completely disagree. Snoop is a better rapper, but not even close as an artist. Dre is a (marginally) better producer, but not much of a rapper himself, writes none of his own lyrics etc.