I don't think comparing an already declined India to Thai is a fair comparison.
See https://ourworldindata.org/grapher/gdp-maddison-project-data...
Based on the Maddison Project data, it looks like India's economy never had a huge shrinking event. It was just outgrown by other economies.
In 1700 India was by far the world's most populous country (using modern borders): https://ourworldindata.org/grapher/population?tab=map&time=1...
High population probably explains India's high GDP share in 1700.
India was always populous, so that was a constant.
You may also like to read about increasing famines in British controlled regions, how food crops were forcibly replaced with cash crops and so on. E.g. https://www.researchgate.net/publication/394628864_An_analys...
Unfortunately not many people understand or appreciate how colonialism destroys a country and they just see the end result and claim that the citizens of the country were incapable of developing by their own.
Not only economical, but also psychological (as in lose of self confidence) and cultural (assuming own culture is somehow inferior to the rulers) destruction happens. It is not much different from abused people losing self confidence and blaming themselves and additionallyhaving to suffer victim blaming from others - just at a nation scale.
Before getting absorbed by East India company, some native kingdoms/empites did start with modernizing their military which indicates there would be a strong effort towards industrialization if it weren't for the British regulations.