Ranking varies by what you measure
- By GDP gives a top 5 of US, China, Japan, Germany, India (UK and France come in 5 and 6 followed by Brazil, Russia is 11)
- By population gives a top 5 of China, India, US, Indonesia, Pakistan (Brazil at 6, Russia comes in at 9, GB at 21)
- By GDP per capita give an intriguing result of Luxemburg, Macau, Switzerland, Norway, Iceland (Ireland is 6 US is 8, UK is 25 and Russia is 64)
Data on Worldometer https://www.worldometers.info/gdp/gdp-by-country/
Great Britain no longer cuts it on any of these.
The US constitution sought to balance population and state power, The House of Representatives is based on population, the Senate has 2 seats per state.