As hoekie said, lets not compare a player that barely troubled the top 50, to someone that actually went top 10.
But I see your point, in that you're probably referring to the fact Spirlea didn't make the most of her opportunities after making it 'big'. Anyway, back to Jana K. I never thought she was that good. Sure, she had flashes of brilliance, but they were few and far between (most players ranked about 50 have those odd flashes occassionally). Maybe she should have had a better career, but I never thought she'd ever trouble the top 20, which she didn't do. Don't think she came close (what was her best rank?).