It’s an interesting article, though it would be better if it had some figures and definitions to back it up – for a start what constitutes a small city. Liverpool currently has a population of over half a million even after decades of decline. Is this big or small?
No-one would argue with London being big, but it declined from about 8.5 to under 7 million over the mid-20th century – that’s like losing two or three Liverpools! – then started growing again (after a lot of the industry had gone away) and is now back to its largest size ever.
The US probably is different because of the huge land area. In much of Europe, I think small cities can still be viable because they are clustered into larger metropolitan areas. Look at the Reinland or the Birmingham area, for example.