GDP still measures the size of the national economy and the created value-add reasonably well. It was never intended to be any kind of quality-of-life metric, even though quality of life can be assumed to grow, at least to a certain point, along with GDP as the general standard of living rises. GDP is a poor metric if it is affected by, for example, international tax avoidance, as in Ireland, but generally speaking, I understand it to be a very good yardstick for the economy.
And roughly, more people = more GDP. More is more! 
There have been problems with people moving from place to place for tens of thousands of years since the last time humanity started spreading across the globe, but generally speaking, economies that are able to dynamically absorb new people into the workforce (and even more importantly, into innovation) seem to be doing reasonably well, while elsewhere growth stalls. It is, of course, a value-based and political choice what one wants from economic growth etc., but that is NOT the topic of this thread. For that, there is this filthy place.
The point in the message above was to raise the risk in this thread that if a similar level of influx of new people does not continue in the USA (it is a really hot political topic there), wage inflation could gain new momentum, which in turn has its own implications for interest rates.