The best 3D character Models/Animations are done by the same person who created them. If someone else does the work it will never bee 100% accurate to what the creator imagined. And if you are good at drawing and concept art getting into 3D isnt a huge step. I mean it isnt realistic in huge companies but it would produce better results.
This is entirely inaccurate. Very brief summary, I can elaborate if need be.
1. Concept art and 3D models are very different fields. The entire field of 3D art is split into its own sub fields. First, learning the software is in itself a pain in the ass. Learning proper topology and edge flow in itself is one of the massive roadblocks that come from modelling characters. Depending on the process that is used, be it High Poly Sculpts, with texture bakes onto low poly retopos or from base "high" poly characters from the start. There are people that are great at doing 2D art but are crap at visualizing or creating interesting imagery and character designs.
2. Surfacing the character (Textures and materials) is its own layer of a pain if you aren't use to how it works, as now a days you don't get hand painted textures. Especially in unreal, where you're doing a lot of combinations of textures with algorithmic nodes that are being used to get the display that you want.
3. Rigging. Understanding proper joint placement, hierarchy, translation into the game engine. Unreal will give you a massive headache if you don't rig properly. Weight painting. All the fancy joints that you want to get procedural or dynamic movement out of that can either be done in engine or in software and exported. The amount of times I've seen exceptional 2D artists go into 3d modelling, manage to get a grasp on that and then collapse at this step is a large number.
4. Animation. ALMOST EVERY PERSON THAT HAS ONLY DRAWN CANNOT ANIMATE. They are extremely different fields. "Drawing" (for lack of a better word at the moment) relates to detail in the individual image, where as animation relates to the overall movement of the sequence. There are some things that are connected, but there are also large separations.
5. The concept artist is not always the person who creates the character. They provide lots of different ideas of what the character could look like that is then passed on and iterated on until it matches the vision of the game. The animations for the game, especially for a fighting game are directly tied to game balance as well.
Basically, what you're saying is that the game designer who designed the character should concept it, model, rig and animate, then implement the character in its entirety, which realistically will not work because of the split in skill between many of the different disciplines. Add in sfx and VA and programming for each of the moves and you might as well have them do the entire game alone.
I understand what you're saying, and sometimes yes, people will have to take on multiple roles and work across different fields in smaller studios. But, there are large drops in quality that in some cases aren't evident because they use tricks such as camera placement in order to make details a lot less noticeable.
It's similar to programming. You can have an engine programmer, a tools programmer, a graphics programmer and a gameplay programmer, and both can technically do each others jobs but each one requires a different set of skills. Engine programmers at the fore front need to know how to properly manage memory and data, where that's not something that's as much of a focus for a gameplay or tools programmer. Graphics programmers need to have an eye for visual details where as an engine programmer might not.
Tl;dr: Most people don't have the skills, and cross specializing while possible still requires time and depending on the difficult of the task, support and help in order to speed up learning.
Source: My job as a game developer and I teach this stuff.
Quick edit: I apologize if came off a bit aggressive. The amount of times I see comments like these ends up frustrating me a ton.