Well I think you need to count Lanzing, Kelly, and Moreci. They were writers on the Nightwing book. Their issues were basically inventory issues used to try and bridge the gap during the change over with the ongoing writers, but I think it would still count. Also I think you need to count the writers scripting too. It would technically look like this if you broke it down:
-Humphries (on for one arc)
-Lanzing & Kelly (one issue)
-Moreci (one issue)
-Percy (one arc + a few other issues)
-Lobdell & Nicieza (one arc + one mini arc that Esquivel was going to script when Nicieza left)
-Jurgens (unknown)
That is basically all within a year and a few months. That is a lot of cycling through creators. The problems do stem from the editors and upper management, no arguing that, but other writers see this won't want to get involved with this book given how messy it is. This kind of changeover is seriously damaging in terms of being able to attract creators. Seeley leaving because he got burnt out and frustrated with the book and Humphries leaving after 1 arc were noteworthy to me. This was all before King's plans of shooting Dick in the head, so I think the book was having problems for a while and they kind of hit the ceiling once Percy left after King fucked up his story. Then it has been DC editors and their reliable in-house writers churning out issues during the Ric arc.