The graph uses average hourly wages which does not include overtime, bonuses, shift premiums, and employer benefits. It also doesn't account for all workers.
https://files.stlouisfed.org/files/htdocs/publications/es/07...
total compensation tracks pretty well.
If I misinterpreted your comment (I think we agree), I welcome your explanation of why purchasing power stays the same when efficiency increases since 1971.
i would expect that purchasing power remains consistent for people doing the same work.
It's true that capital gains is captured by those who own the capital - but those who do own such capital had to take capital risk to obtain such gains.
Labour income (aka, wage income) increased if the labour changed to be more efficient without said use of capital - for example, programmers' income is very high. But for someone whose labour output hasn't changed from the 70's, is it expected that their purchasing power somehow increases (compared to someone else's)?
I still see graphs as these https://wtfhappenedin1971home.files.wordpress.com/2020/06/im... as clearly saying labour compensation correlated with advances in technology until 1971, when there was a dramatic shift, and that this is also the time when supply of $ was put in the hands of central bankers rather than any real and external asset.