The World Economic Forum’s Davos summit has confirmed the obvious that the prospective global boom is over. “Is that it?” might be the repost to the International Monetary Fund’s latest downgrade. Sure, 3.5% global growth is still impressive and better than a couple of years ago when the IMF hailed “the broadest synchronised global growth upsurge” since 2010. The real story of global growth is the serial disappointments that have dogged this expansion from the start. For advanced economies, it has…