I overall agree with you, but to be completely honest, I actually do think they would be able to write a decent black character if they had to.
The reason for that is because of the way the game handles the refugees, at least as far as I got into it. From what I know (from Era, didn't go around digging too much), the dude is also against the current influx of refugees in Europe, so when someone said that the game has NPCs talking about "damn refugees disturbing the peace", it really made me worry.
But, playing the game itself, I was surprised to find out that things are not quite what they seemed. They had the perfect opportunity to do commentary on the current refugee crisis using a historical setting as a mirror, but the game actually very clearly paints them as victims and sides with them. The NPC dialogue bashing them is indeed there, and not only one, almost all of the townsfolk you can talk to and ask what they think of the refugees will have a negative view, and at most will say "I know they went through a lot, but...", but what the person who brought that to my attention didn't know (they were only watching a stream while that happened) was that YOU are the refugee. Your friends and relatives are the refugees. They are absolutely painted as victims of a war they had nothing to do with.
You see firsthand them losing their houses, families, workplaces, and being forced to take refuge in another town, and become beggars at that. It's even telling in the mechanics: These townsfolk who discriminate against them have their names as "Townsfolk" over the interact prompt, while each beggar that would in any other game just be "NPC_Beggar" at most, here they have a name, because they're the people Henry knew and grew up with, they're your friends, victims of the horrors of war, living in a terrible situation. Even Kunesh, who already had nothing at the beginning of the game in Skalitz (which was by the way a really cool piece of environmental storytelling, in my opinion), ended up in an even worse situation as a refugee.
This is already a pretty major aspect where the game's message was without a doubt not a mirror to the creator's own beliefs, which seriously surprised me.
That being said, I do think for this particular game, with the examples people defending the inclusion of diversity can give being terrible, it wouldn't really work out that well. But if they decide to have a black protagonist for their next project for whatever reason, I don't think it'll necessarily be terrible, despite of Vavra's own racist beliefs.
It's also possible that if the game was actually about the current day refugees the message would be quite different, though, and in that case you'd be completely right.
