>>38818851People can make convincing designs that would make great designs in game, but many fakemon artists commit mistakes. One is they just wing it with one or two designs without giving it time to cook and develop to become finalized, another is that they design a fakemon as a character rather than what would be a species. I'd say one of the major things is a fakemon artist is typically alone drawing, whereas designers for GF go over designs back and forth as a team while considering things like animation, modelling, toys, etc.
The designs have to evolve over time I mean it's a decades old franchise, and I'm not sure what kind of design bible or philosophy the team goes with when adding members. But if you see some of the drafts like Hydreigon especially you'll see how important giving a design time and critique will change it. Sugimori talks about a "balance" as well. But most people judge harshly without having any sense of design, or because a design isn't stylized in the official or anime rendered look. Simply being a fakemon in general already redflags most people to reject it when you don't know what GF is going to put on the table next.