Sales is a terrible way of judging quality. Justin Bieber sells a shit ton of albums. Is that "quality"?
McDonald's sells a shit ton of hamburgers. Are they "quality"?
I agree, that was just in reference to popularity more than anything. Kanye has been more popular than L'il Wayne and every one else for the past 5-10 years and that was the easiest way to show it.
Some non-Kanye rappers that are good:
Lupe Fiasco - first two albums are great, last two not so great. Check out the The Coolest
Kendrick Lamar - already mentioned, but everything he has done so far has been pretty great.
MF Doom - Madvillainy is really good along with MM..Food. Check out All Caps
J. Cole - his first two mixtapes were good (Friday Night Lights and The Warmup). Check out Premeditated Murder.