There’s only one valid reason, they walled off too much power into voidform increasing it with the 3x chorus build. PvP is fairly tough with that. Hulk-out things are fun but they went too far with it. Well, also, the cast time. Entering void form should have zero cast time, even better off the GCD.
As a timed transformation it was fine. With increasing gear you could keep in form longer and longer and with endgame gear one was in it all the time. It only took 2-4 casts to get back into it.
Also - voidform did a job very well. Prior to voidform sPriests had a very bad problem for a very long time. The rotations were so boring. The class played badly, really badly. Where that most showed was in long bossfights, it made me want to scream sometimes. Boring boring boring. Voidform as a timed transformation that one could extend with better gear and playing, fixed that very well.