PD: I just checked the numbers. I found this: https://www.uscis.gov/sites/default/files/document/data/h-1b.... Indians and Chinese make up to 90% of H-1B petitioners.
The Indian numbers are "inflated" as their backlog is high (i.e. they have to petition to renew their H-1B multiple times) - so for example if it takes 12 years for an Indian to get the GC, they petitioned 4-5 times and the "equivalent" percentage is really about a quarter of the figure shown. Whereas a South Korean likely will get the GC without petitioning a second time, so their numbers remain small.
Put another way, if the wait times for Indians was under 3 years, then about 75% or more of the people listed in the Indian count would have gotten their GC a while ago, and would not be counted.
When you adjust for this inflation, it's not obvious that India + China is > 50%. Nevertheless, I agree it is a significant percentage.