Exactly.
Except all the ones I and others have already mentioned.
Those are indeed the people on their land.
The orcs aren't racist at all, reasoned or otherwise. They're isolationist. They do not discriminate based on racial features, they discriminate based on in/out group. This is like saying the women only train cars in Japan are sexist.
Proventus is, indeed, a prejudiced individual. Tullius does not appear to be motivated by racial prejudice, just disdain for those he views as traitors. He's a soldier, through and through. Loyal to the Empire to a fault.
Their entire platform is built on "returning to the old ways". That is, by definition, regressive.
I've already explained why that is.
And Windhelm is...what? Oh yes, the most staunchly traditionalist Nord city and the seat of Stormcloak power. And it seems really convenient that the problems are "economic" in nature yet seem to only affect a singular racial sub-group.
An issue with this discussion is that I cannot draw on the very clear real world parallels at play to illustrate my point, but the talking points you're using are...disturbing in how familiar they are.