This is a very astute question. The latest and most detailed quantitative studies suggest that the beginning of the Great Divergence precedes colonization, and that this is true even if you compare the richest regions of China (the lower Yangzi) or India (Bengal) with the richest parts of Europe, which would be England and the Netherlands.

The "early" great divergence literature, notably Pomeranz, emphasizes the similarities between China and Europe until at least 1800. But more recent studies have tried to measure this in more detail, and generally returned to the conclusion that China was not at the same level of development. Bozhong Li and Jan Luiten van Zanden, "Before the Great Divergence? Comparing the Yangzi Delta and the Netherlands at the Beginning of the Nineteenth Century," which (as it says on the tin) provides direct estimates of GDP for both regions broken down by sector. The finding is that, while agricultural productivity was not dissimilar, there were large differences in manufacturing and services productivity, such that the Netherlands had nearly twice the GDP/capita of the lower Yangzi. Whatever the similarities between these economies, by the 1820s at least, there was a very substantial difference in incomes.

The case for Bengal being approximately on the same level as the richer parts of Europe was suggested by Parasarathi, and indeed one can find (like in China) a plausible case based on a qualitative, holistic approach. But more careful measurement of living standards, as measured by wages and prices, brings back the gap. Pim Zwart and Jan Lucassen have just published "Poverty or prosperity in northern India? New evidence on real wages, 1590s–1870s" in the Economic History Review, which shows real wages diverging in the late 17th century, with quite a substantial gap between the higher-wage parts of Europe and Bengal by the time of colonization. This is in line with earlier findings by Broadberry and Gupta, Allen and Studer, and Tirthankar Roy. Bengal appears well-integrated into world markets for luxury goods, due to its impressive artisanal textiles industry. But the overall picture is still a region with relatively low wages and disintegrated markets in the countryside, which in a predominantly agricultural society is almost certain to lead to low overall incomes.

And so, the latest round of scholarship has pointed towards an earlier Great Divergence. Pomeranz and Parasarathi have written an essay in Roy and Riello's Global Economic History, summarizing the state of the debate and to some extent reinforcing their positions. Both scholars still gesture towards late-ish divergence, from perhaps 1750, though even this rests more on critiquing their critics and pointing to possible ways their argument could still be correct, rather than building a solid case for carefully measured equality.

Perhaps new data will further refine our picture, or perhaps (as Deng and O'Brien suggest) it's a giant mess prior to the 20th century, and this is all a bit of a fool's errand to try and reconstruct GDP with accuracy good enough for comparison - the best we might be able to say with absolute confidence is that these economies were all quite different. But I think the case that these regions had equal incomes even as late as 1750 seems, on the weight of the evidence, quite unlikely. At the very least, the case for late divergence is on the back foot, and would need to produce some substantial, measurable evidence for their claimed equality.