I could be wrong, but I've always felt that the college to WNBA transition is slightly easier for good posts than it is for good guards. It's never actually easy, mind you. All players have an adjustment period.
For guards, I think their 2nd year as a pro is a better indication of their potential.
An interesting and insightful post. I tend to agree with you and I think it has to do with the speed of the game and the competition. Post players especially those who live at the low block need to be good at catching and shooting, they are not expected to handle the ball much, nor be great passers. In transition to the pro game the physicality goes up a notch, and the defensive size/strength does too, but the speed and quickness is not that significant an issue for them.
For wing players the transition involves size, strength, speed, and quickness - passes they made in college are intercepted, ball handling they could get away with results in steals.
And the old adage of 'you can't teach size' really does come to the front.
I also think it explains why post players like Appel and Dolson struggle a little more than players like Charles and Stokes - their college games depended on the passing and ball handling that distinguished them from other college post players, and they struggle in the same way wing player do with the speed/quickness of the pro game. I have been a little surprised at the Asst/TO numbers for Dolson as a pro based on what she was doing in college - this maybe explains it.