While I'm 80% sure those are real, I'm also kinda iffy because they were leaked so ridiculously early, whereas we didn't really know most of the starter evolutions until like...usually a month or two before release in prior generations, didn't we? It's kinda odd, but it's even stranger that as more leaks surface, they're pretty consistent with the descriptions of the starter evolutions, making the initial leak of the final starter evos even more likely to be real.
It is very interesting because starters' final evolutions have never been leaked this early before, and like you said the starter evolutions usually don't surface until close to release date. Given the concept art was part of a Chinese leak that accurately predicted a lot of stuff that was revealed in recent trailers, it is likely going to be real and that means 7th Gen will go down as the earliest point during pre-release that the new generation's starter evolutions surfaced, since June (which was when the art first surfaced) was only 3 months into the pre-release since S/M's announcement.