I read the Bitcoin Standard and had this question about Keynesian economics?

In the book, it argues that when you have a deflationary currency (gold, bitcoin) as the world reserve, it encourages saving for multiple generations and has inspired many great human feats such as the Sistine Chapel and the industrial revolution.

Meanwhile, an inflationary currency as the world reserve leads to society going for a quick buck (suburban sprawl destroying farmland/nautral land in favor of houses that take up too much space, goods built to be thrown away, less incentive to save due to savings being debased, etc)

However, I do think that Keynesian economics has somewhat of a point when they say: An inflationary currency encourages spending, which spurs up economic activity due to the money being recirculated into the economy. Whereas a deflationary currency encourages hoarding of economic energy, and not recirculating it back into the economy.

Is this a valid argument? Why is it not a valid argument?