While France's credit rating downgrade on Friday generated politically charged headlines, the bigger surprise was Spain's upgrade which got far less attention. An even bigger story is euro credit convergence and the disappearance of the long-standing dichotomy between the region's core and its periphery.

Germany may be clinging to its prized AAA sovereign credit rating - which could soon be in jeopardy given the country's planned fiscal boost and debt spree - but euro zone sovereign credit ratings' weighted average appears to be gravitating to a high single-A.

GDP-weighting flatters that average a bit because Germany accounts for almost a quarter of the bloc's economic output, but there's little doubt the other big euro nations are closing in on single-A - roughly where credit default swaps currently price the effective U.S. sovereign rating.

Graphics are produced by Reuters.

That's a far cry from the reality just before the global banking crash and subsequent euro debt crisis 18 years ago, when Germany, France, Spain and five other euro sovereigns commanded AAAs. But the single-A average mirrors the deterioration in public credit ratings around the world.

If the final remaining top-rated European countries eventually start to slip towards that new centre of gravity - as now seems likely given that the long-standing German debt brake has been lifted and defence spending prioritised - cheaper joint borrowing at a rating of AA or above may start to look much more attractive, even for the sceptics.

Germany, the Netherlands, Ireland and Luxembourg are now the only countries that still hold at least one AAA from the three main credit firms. The other nations have suffered in recent years.