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That's a massive strawman and a pretty lazy falacy to use: it's like saying that CEOs cutting jobs to boost short term bonuses is a "vast conspiracy" or that politicians lying is "a vast conspiracy".

As if people influencing people and people doing what's best for themselves requires them to all coordinate with each other forming a "vast cospiracy".

As soon as the heads of the institutions that produce economic figures are nominated by politicians, both the ones nominated are the ones expected to be friendly to the interests of those politicians and the ones in there will be under political pressure. Politicians want to look good and win elections and they'll put pressure on those who produce politically important figures to make those figures look good so that they look good - no conspiracy required - and, guess what, GDP Growth has been a politicially important figure for several decades now, as noticed by the loud celebrations from whomever is in power that GDP is growing.

As for the numbers: here's a pretty chart. Notice that's the median, which is the correct average to reflect the experience of most people since the numbers aren't skewed up by a small fraction of high-earners, unlike the mean.

Observe how in the 60s a single factory worker salary was enough for a house, a car, a family of 4, whilst now it takes two degree level salaries to get the same with smaller families - feel free to explain why what we are told is equivalent to 2x the salary back in the 60s buys less that half as much.

Keep in mind that any "beautification" of those figures was not be massive: we're talking about in average maybe 1-2% a year. It's just that over the span of half a century or more it significantly adds up.