"It's complicated" is a far better line than the more ideological, 'but people on welfare have fridges and TVs!'
It is true that 'standard of living' cannot be captured entirely with the data we have available nor with a single measure like median income.
Suppose we could agree on 10 metrics or 20 metrics. It is unlikely that improvement for some period of time would be constant or universal. Of whatever 10 metrics, we might see a linear improvement in 2, no change in 5, a negative change in 2 and 1 big change in some other metric. In my example, we have assumed a common set of measures. However, in this type of conversation, commentators usually point to commonly understood measures like wage increases compared to inflation or a difference between increases in life-expectancy and some expected increase in life expectancy given money spent on health care etc. The problem with these measures is that they can be misleading but seem objective. In part, this is the author's claim, that whole new technologies might come into existence in a period, but might not be reflected in some living standard measure.
However, while it can be insufferable that many pundits and analysts mouth very similar lines about the falling middle class, it doesn't mean they are wrong. A critique of the invocation of living standards is peculiar in that measures of productivity etc are objective, while lived experience is not. But while lived experiences are subjective it is more important that they are RELATIVE. Who experiences a higher standard of living Andrew Carnegie or the McDonald's employee watching YouTube videos during his lunch break?
When commentators mention that wages have been stagnant for decades and that new jobs added to the economy are low wage etc. they are right that living standards are at best stagnant or dropping. Why? New technologies are not radically making life easier/ healthier. Instead new technologies are playing a large role in keeping wages and the possibility for wage growth low, by eliminating or automating jobs. They also create the expectation that wages and other areas of life will also not improve, which has other effects. (Ex. If you believe you will not see wage increases, you will not try to buy a car or a house.) The certainty among many Americans that they cannot improve their circumstances creates unease, anxiety and a loss of control. Eventually, this translates into lower voter turn-out, into a decline in the base of supporters of civil society etc.
If in 20 years the majority of Americans were making minimum wage and had to spend time filling out forms to get government assistance for food, health care and housing subsidies, if they had even fewer friends and family than they do today, because scheduling became more difficult in a "flexible hours" economy, but we had holographic displays on our smartphones and life expectancy (and the retirement age) increased by a couple years, would we say that living standards increased over a 20 year period?