And larger GDP does not necessarily mean less poverty or less inequality. but a shrunken GDP does tend to very mean the opposite. GDP is the size of the economic cake but does not dictate how it is cut - and excludes many other factors.
But If you measure GDP per capita the top countries are luxemburg, switzerland and norway whilst the lowest are Central African Republic, Burundi and the Democratic Republic of the Congo - so there clearly is a relation between it and quality of life overall.
China has a massive GDP compared to the UK cos its population is something like 15 times greater. its per capita GDP is 73rd compared to the UK's 26th. If its gross GDP dropped to the uk's level it would mean abject poverty and starvation.
but yeah - its a crude measure - ireland's per capita GDP is 5th - which doesn't square with general levels of affluence. Unless it all Bono's piles of loot distorting the figures.