As far as the productivity gap goes. Workers are more productive because of the tools the business owners acquire for their use. As such, the numbers are inaccurate for any worker that does not buy their own tools to use in the business.
The productivity tool is a laptop which costs perhaps $1k. It is neither here nor there who buys the laptop - it’s only $1k. It is what you do with the laptop that matters.
I do not know how strong this effect is, but I doubt it's being sufficiently (or at all) considered given that there is literally zero mention of it. Alas, to me this metric seems like either a lack of statistical understanding or political use of statistics.
If there's an oversupply of workers who can use tools that leverage productivity doing the same tasks then naturally they will earn less.
That means that people are learning the wrong things more than anything though.
People have to learn that when there's an oversupply they should look for other avenues where they can leverage their income better. Too much supply lowers your relative productivity substantially, as such I dispute the claim that worker productivity has gone up. Given the sheer amount of low level tasks I'd lean towards assuming that it remained largely constant.
Also, the productivity tool is not just a laptop. Software, data, data processing (cloud computing) in the case of IT jobs are just some factors that the worker has no ownership of and thus can't be accredited with the increase in productivity that these provide.