" British South Africa vs Apartheid South Africa"

I will leave it to someone more knowledgeable to talk about Southeast Asia, but I feel like I need to speak up about southern Africa, because I think this is a false comparison.

If we're specifically talking about Apartheid South Africa, we're talking about a system of racial laws that were instituted after the 1948 South African elections, and dismantled in the late 1980s-early 1990s, more or less ending with the ANC victory in the 1994 election (although vast racial disparities continue to this day). I find it hard to specifically blame that on Dutch colonial rule given that the Dutch specifically only controlled a Cape colony (roughly similar in area to today's Western Cape), and that was occupied by the British in 1806, and formally ceded to Britain in 1814, almost a century and a half before 1948. The Dutch never controlled areas like KwaZulu-Natal, Transvaal or Free State.

Of course, those areas were conquered and settled by Afrikaner Voortrekkers in the 19th century. But there's two points here. It's inaccurate to call Afrikaners "Dutch" as if the two nationalities were synonymous. Afrikaans is a separate language from Dutch, not a regional dialect, and so while I personally can't speak to their mutual intelligibility between native speakers this is different even from, say, American English and British English, and even with that example it would be a little inaccurate if we were talking about Anglo American colonialism as synonymous with British Colonialism.

Another point of inaccuracy is that if we're talking about British South Africa as specifically South Africa as a British colony, versus Apartheid South Africa after 1948, it's not exactly different people. Meaning it's not like South Africa was run by Brits or English speakers prior to 1948 and Afrikaners after. It was mostly Afrikaners in both periods.

A specific example would be Jan Smuts. Smuts was born in Capetown, moved to Transvaal, and worked with the Transvaal government during the Second Boer War, eventually even commanding troops in the later stages of the war. After the war's end, the Union of South Africa was negotiated and initiated by 1910, which combined the then-four British colonies in South Africa into a self-governing Dominion in the British Empire, similar in ways to Canada, New Zealand or Australia. Louis Botha (a former Transvaal Prime Minister and Boer War general) became the first Prime Minister of the Union, but Smuts was part of his government, and would later be Prime Minister himself for huge chunks of the period before 1948. Which is to say, the British Empire Dominion was largely run by Afrikaners.

So what changed in 1948? Basically a paradigm-shifting election upset. Without getting too into the weeds, Smuts at the time was still Prime Minister, and in charge of the United Party. South Africa at this point had an almost completely whites-only electorate and quite a degree of segregation, but there were fears among segments of the white electorate that the United Party would give in to gradual changes to this. The National Party promised much stricter segregation, and won a legislative majority with a minority of the vote (much less than votes for the United Party), mostly by winning rural electoral districts. I leave it to the reader to draw any comparisons there to other countries and their elections. The National Party would go on to win every South African election until 1994, and to construct (and eventually dismantle) the legal framework for Apartheid.

Even a comparison between British Southern Africa (so not South Africa Proper) and Apartheid South Africa is probably not really useful. For most of the British possessions in Southern Africa had extremely tiny resident white populations, and the one exception - Southern Rhodesia - had a system of white rule that was similar to South Africa's. You could argue that Rhodesia was in many ways worse, as the white population was smaller - something like 5% of the total population at most, compared to white South Africans making up about 20% of the population in 1910 and 10% in 1990, and was very violent in its initial conquest of the territory and in the maintenance of control from 1965 to 1980.

So - I don't think we can really discuss Apartheid South Africa when comparing how the Dutch colonial and British colonial empires were run. Dutch colonial rule was restricted to the Cape Colony (a possession of the Dutch East India Company) from the 1650s to the early 19th century, and many of its particulars of that period (warfare against indigenous people, use of slave labor and an expanding settlement of white "free citizens") honestly wasn't qualitatively different from British colonies of the 17th and 18th centuries.