Jean-Claude Juncker has led his country for nearly two decades.
But some say the 58-year-old has spent too much time on EU affairs.
Juncker, an early cheerleader for the single currency, eventually chaired the informal meetings of eurozone finance ministers.
Pascal De Wit of the Université Libre de Bruxelles said: “ It is clear that he has a lot more influence on the European stage than many other prime ministers and so he’s taken on a lot of EU business.”
“But you have to say that it’s not the same to be premier of a small country. It’s an important job, but not the same as being German chancellor or the president of France.”
That view is partly shared by Juncker’s political allies.
“Of course becoming head of the Eurogroup took a great amount of his time, but I am reassured that he dealt with the Eurogroup and the euro,” said Astrid Lulling, a centre-right MEP from the Grand Duchy. “It is essential for Luxembourg that the euro survives.
Juncker had coveted the the job of European Council president in 2009, but his bid was opposed by former French leader Nicolas Sarkozy and German Chancellor Angela Merkel.