It makes sense. They probably couldn't use Robin (he was in Super Friends, which was still making new episodes at the time), and without him there, who makes sense to take over? Changeling was the youngest team member, and Starfire, Cyborg and Raven were all rookies. Donna is the experienced hand, along with Kid Flash - but Wally might not even have been there, depending when this was (he was replaced by Jericho in 1984, at the same time that Dick became Nightwing).