Unfortunately it happens alot in the game dev within visual novel stuff, that artist that start with the project being invested but over time they grew tired and dissinterested, its pretty noticable within the art of LD, especialy the longer the stuff goes on, yes he did alot of sprites, but over time you clearly start seeing the decline in terms of amount of CGs, since artist were not not involved with project himself, and Hyao clearly need someone who not only likes the game but also the one that would be interest going thu the game and find the moments that can be illustrated
As of right now from what Stan said he often find those moments himself and then approach Hyao about doing them ( or doing them as fanart and offering Hyao to put them in the game if he see them fit ), and that is beside the new moments that based on the ideas that comes up from new artist artwork ( example is Celeb drunk scene that was made from the art of Celeb that he did and later on scene was created for it )
Also same thing with more recent stuff like Orc Wrestling event, as he stated originaly there was no plansto have any CGs in it, but Stan uproached Virile about making CG from Maul for that event ( since it was new character and he find him funny ), which in turn led to another 3 CGs
Hyao need people that gonna be invested in the project and will help with working on it, and not a contructed worker that doesnt involve themself with it till they get asked,
Did ZoroJ art was good? Yes
Does he missed out on working with him? Not realy since he wasnt that invested in it, as much as Hyao need for artist to be investe ( and its not a flaw of the artist but Hyao himself, and thats why he need someone who can take a step and help him with it )