I’m wondering if there really was some bizarre 1890’s psuedo-intellectual/psuedo-scientific movement among like, British fancylads or something, to excuse a lot of recent colonizations… “Oh if they were there 100,000 years ago this colony business would be bad, but 30,000 years? They’re practically squatters pip pip cheerio”

no that wouldn't have made any difference to their thinking either way if anything them being there longer would be a sign they might have built up some real wealth there that would entice conquest and theft even more. The colonial powers only respected the ability to defend territory with force as a compelling factor. Which brought them to the table with Shaka Zulu as an equal despite his country being birthed in his own lifetime

In the works of Rudyard Kipling for example the notion of a treasure placed there by Alexander the Great in his own conquest of India is an enticing factor for conquest. China was acknowledged as a civilisation far older than Europe but once the European powers smelled blood in the water that was no deterent to colonial exploitation