Exactly, people really don't understand how concept art works. Everything they do, everything devs make has had tons of art that needed to be looked at and approved to build up to the end result.
When making early concept art, it's "throw everything at the general idea and see what sticks". You don't have to be too worried about how something will animate or how well skins can be made for it or w/e, you're just coming up with the most interesting ideas that cross your mind.
If you show people early concept art, they will assume, "that's what they were supposed to look like!". If you show people finalized concept art you're working from without the in game models on display, they will think, "Oh, they have time to change it to my liking!". So yeah, anything short of some in game character models would be too lil and would just muddy the waters.
Again, that mural is not "unreliable early concept art". It's cannon in game art that's supposed to be made by the people of that world and culture. And IDK why you quote "artbook" like that, it's literally an art book full of finalized concept art. Like, it only shows the finalized version of Y'shtola's outfit, yet I can find early art showing the development process of her outfit in some fan fest vod. The art team members actually write that they love making these books to show what bosses look like because you may not be able to appreciate the details when fighting them.
As for your questions ...
1-What makes more sense, finishing Male Viera or Female Hrothgar first? The whole reason they felt they were able to make both was because they decided to stagger their releases as to not put too much strain on the team, and the people who got them to do it were the Male Viera fans. We have absolutely no idea when they started putting ink-to-paper on Hrothgals other than "They decided to make Male Viera and Female Hrothgar around 6 months after the release of ShB". That would still have been at least a half year before they released the patch with the Mural in it.
2- This aint OverWatch or LoL, it's a MMO with a pretty rigid CC system. They don't have the freedom to make w/e body type they can think of without running into huge problems. W/e they make is going to use Middie female bod as a base, just like every non-lala female in this game. They can easily know that they want Hrothgals to be "tall-but-still-shorter than Femroe with slim & very feminine forms and pretty cat features" without having tackled every aspect of the design process to completion.
Like, that mural doesn't tell us much about them other than general body stuff that shouldn't be shocking.
It doesn't show us their hairstyles or the style of their 4 faces. Doesn't show how fur patterns would work on them or what CC face features they would have (Like cool scars or face markings. Or if they get horns and is so, where do these horns spout from and so on). For all we know, they can be deciding if Hrothgals get full body fur patterns and no fur patches, or if their fur patches are in different areas. Hell, unlike the males they know that they're gonna give em shared hair as they make them, so that may factor into their designs.
3- You seem to be going with the notion that they're just now figuring out the concept for the full body and have 2 options to pick from. I read what he said, reads more like they settled on 2 faces to me, unless you think they're making some Human clans situation and are making 2 body shapes (they need 4 designs for the faces, and they don't finalize all the faces at once. Like how with the males, they settled on Face 4 and Face 2 and used those as the base for the race, picking the other 2 faces after playing with more concepts that matched that style)