I didnt speak to kv-8s and hetzers because I dont have experience using them. Im not saying that they wouldnt be a problem, they could be. But ostwinds most definitely would be a problem.
You dont have to stop centaurs, kv1s, or churchills when you can consistently stomp games before they come out, thats how the build worked.
A lot of those nerfs you mentioned to okw stuff arent too relevant because the point of the build is that the mechanized units alone (pumas and ostwinds) would do all the work for you. More than that, why even change the ostwind or the m10 to begin with? Its a step in the wrong direction.
Because both the ostwind and m10 offer very little with their new high tech cost (especially the ostwind with the cheaper P4 and the more effective AAHT).
Once more in the case of the OKW imo these vehicles should be available even if the T4 is destroyed.