Using the title argument surely Smashnova with her 19 is one of the greatest players to never win a slam
Apart from Smashnova Kournikova lost her finals to Venus and Hingis whereas Nicole beat Granville, Razzano, Peng and Tati (by retirement) plus when Kournikova was losing in Tier I and II she was losing in QF and SF to people like Hingis, Venus, Seles, Graf, Davenport, and Pierce all slam winners.
Maybe this thread should be WWW: Peak Stacey Tan vs Peak Bruna Colosio. No way would Anna lose 6-2, 6-1 to Stacey Tan who never even made Top 500. When you take their most embarrassing losses at least Colosio was a Top 300 player.
I personally like Nicole but to say she is immensely better than Kournikova is ridiculous, had Anna played in the same era she would have had a similar if not better career than Nicole, Anna's years on tour were possibly the toughest, whereas Nicole was peaking 2006-2008 a pretty weak time for the WTA.