You can measure happiness with numbers. You can measure anything with numbers. I've welcomed you to provide your favorite happiness metric. But instead you insist that happiness cannot be measured in numbers. Anti-science attitude on display.
You cannot measure everything with numbers. Many things in life cannot even be ordered[0]. Lives are different. Yes, some are just worse/more challenging than others, but in general people and their experiences are wayyyyyyy too complex and multivaried to be projected onto the real line. Only by narrowing your understanding and experience of life to measurable phenomena like bank account balance can you actually do the comparison you're looking for. And then you've all but ruined your life.
To address your point, GDP per capita is not a good metric capturing happiness, for several reasons. Most trivially, because it does nothing to reflect the distribution of wealth. A country could (purely hypothetically ;) ) have massive GDP per capita but the benefits flow mainly to the top.
Even putting that aside, a culture with massive GDP but where the citizens don't have the time, peace, values, and social structures to enjoy life is not a happy society.
