Diggins deserved to be in the 3 to see. The professional game is extremely hard on small guards, particularly small guards that get picked by bad teams with undevloped offensive systems. Succeeding at that height and size takes technical proficiency that must be learned. Anyone with any awareness of the difficulty of that transition would be expecting her to struggle as a rookie. Just look at the history of both the WNBA as well as the NBA.
I'm not buying it. Neither Bird nor Whalen "struggled" in their rookie seasons and both are 5'9", same height as Diggins. Bird averaged 14+ PPG, about 6 APG, and started all 32 games, and Whalen averaged 8+ PPG and just about 5 APG. Her A/TO ratio was not great (5/3), but neither were ever benched like Diggins was.
Cappie Pondexter averaged over 19 PPG her rookie campaign and Piph Prince was almost 10 PPG her first year. Neither are true PG's, but with Skyler's supposed "scoring" acumen, she certainly could play the off guard spot if she were more effective on the court. And by the way Cappie is also 5'9" but Prince is listed at 5'7". And both Pondexter and Prince started every game their rookie year. So I don't get the "small guard" excuse, or that anyone really expected Diggins to struggle...
I don't know where any of those players went in the draft (Bird went #1, Pondexter went #2), but I'm not sure if any of them were hyped as much as Diggins was.
Lastly, Goodrich is also a rookie. and she's 5'4", yet she replaced Diggins in the starting lineup. Your logic makes no sense. I guess the game is less hard on her?