Hard to say whether the title name played a part in Grayson's sales without access to DC's market data but I'm inclined to believe this is the case. Brand recognition matters, especially in this industry (it seems infinitely more important for comics than most businesses) and "Grayson" doesn't have the brand value that "Nightwing" does. So yeah, I figure if they had done Grayson and all the Spyral stuff, but kept Dick in costume and using the Nightwing name, sales would've been higher. And Grayson still saw a decent increase in sales for a big chunk of its run, as I recall. To this day I suspect that "Nightwing: Agent of Spyral" might've been Dick's big break.....but the lack of recognizable visual markers made the community (if not DC itself) see it as a temporary gimmick rather than a viable, sustainable status quo.
Granted, it wouldn't have made a ton of sense for Dick to retain the costume and name while he's "undercover" as a spy.......but it didn't make a ton of sense for Spyral to recruit a dedicated and experienced hero who's also one of the world's most eligible (and handsome) bachelors either.
Retroactive context maybe. Even if this turns out to be true and Dick is behind the Leviathan event (which I very much doubt) I cannot believe DC had the foresight to play "Ric" off as a narrative device to make fans more open to the idea of Leviathan-Wing.