I don't think Jen and Venus have underachieved at all. These women have won Slams and been No. 1.
Yeah Jennifer could win more titles on a regular basis, but in terms of GS results and rankings, etc. she has really excelled.
Amelie and Elena D spring to mind. Amelie made a GS final and its true, she hasn't made another since. She is now 24 and time is ticking. She really has to get it all together and give one big push. 10 titles is pretty small for someone like Amelie who has the ability to win so many.
Elena D reached a GS semi-final and announced herself. She then fell out of the Top 10 for over 2 years. I feel she should have been wiser regarding her tennis and been a Top 10 stalwart by now and built on her Slam success.
Rubin, back in the day of 1996, maybe could have won a Slam. Injuries blighted her career. But being in the Top 10 now is a great acheivement for Chanda. In today's game she has performed to her maximum level as her weapons just don't bring her much success CONSISTENTLY against the very top. A few excellent wins, but nothing to really show for it.