Well, the entire point of the NP was to run SA along the interests of the Afrikaners. That is why the miner unions and guild type small business groups (with limited membership) along with the farmers were always the recipient of state largesse, while the middle and upper middle classes of the Afrikaners were buffetted by the civil service and nationalized industries. Inequality within the desired grouping wasn't really the objective; the advancement of its material interests were (DF Malan had stated that he wanted every member of the Mine Worker Union to have access to vacation and cheap domestic servants, for example)
But SA even before sanctions, ran into the same issue that the UK, US, France, Israel, etc. ran into by the late 70s, which is that such a system is not sustainable when you blatantly ignore market forces, and is even less sustainable when you are excluding 85-90% of potential economic actors. It was only when PW Botha made small moves towards economic liberalism (because he saw that in a commodity exporting economy like SA, you will fail and fail quickly when investment dries up), that you saw a real break up along the NP's flanks. The HNP and KP both disagreed on political reform, but the KP wanted a genuine opening up of the market while the HNP wanted to double down on egalitarian ethnonationalism. The Nats stood for little besides perpetuation of itself by that point in time.
Yeah I had forgotten to include that about the Progs. I find it odd how liberalism never really had a whiff of power at the national level. At the local level, the Progs and the DA have obviously been more successful than the Nats and ANC were,
especially in Cape Town and Pretoria, but it has never translated to national popularity.
It is interesting how many of the Nats ideas the ANC ended up copying. They are looking at bringing back proscribed assets, for example, and have a similar fetish for insourcing policies, ethnic favoritism, and nationalized industries (and bailing them out with public money).