People think otherwise because they have a special (very lengthy) backlog for Indians, and to some extent Chinese. Until about 2018, if you were from another country, 3 years was longer than the average to convert H-1B to a Green Card. Lots of people would get it in less than 2 years.
I'm still not really sure why there's such a strict limit on green cards per country of origin, when countries have such a wide variety of population or even area. What if India decided they wanted to make things easier for expatriates as well as increase their influence wherever number of countries count and break into the 28 states and 8 union territories.
Suddenly, they could get a 35 more votes at the UN and a ton more green cards. They could all be individual countries, under the banner of the Indian Union which sets fiscal policy and manages the currency and provide for common defense. There's plenty of space in the ISO 3166-1 alpha-2 namespace for 36 new entities, and there's lots of good reasons to do it!
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.