This is key;
"In a year or two, Rakestraw and Arnold could be the starting outside cornerbacks in a Lions defense that has other good talent on that side of the ball to help their cover corners."
Rookie corners usually struggle their first season. And the Lions history with bringing rookies along slowly are all excellent points in establishing them so they get confidence. Nobody in the organization wants to throw them to the wolves and ruin their careers. By the end of the season, they should be playing at a high level, just in time for the playoffs...😀