Here is a random real-life sampling. 1st round picks from the 2008 draft who were taken as starters and what % of appearances were starts. Only 2 are above 50%.
Code:
# Name Team Games Starts %
28 Gerrit Cole New York Yankees 132 132 100%
19 Andrew Cashner Chicago Cubs 235 142 60%
30 Casey Kelly Boston Red Sox 19 9 47%
15 Ethan Martin Los Angeles Dodgers 17 8 47%
25 C. Friedrich Colorado Rockies 124 42 34%
4 Brian Matusz Baltimore Orioles 280 69 25%
27 C.Gutiérrez Minnesota Twins 142 32 23%
9 Aaron Crow Washington Nationals 254 0 0%