Jon Arryn is normally believed to have been a wise and capable administrator in the fandom. Generally there are two reasons given for that assumption:
- He kept the peace for most of his tenure.
- He gave the realm years of plenty.
But it appears to me that keeping the peace wasn't really much of an achievement. Westeros had just recovered from a horrific civil war and evidently everyone was too exhausted to start another war on the continent. Off-Continent, the Greyjoys, who mostly stayed out of Robert's Rebellion, except for the minor raids off the Tyrell coast, did rebel and Jon Arryn isn't mentioned at all in the campaign and it appears that King Robert, Eddard Stark, Stannis Baratheon and Tywin Lannister sorted out the Greyjoy rebellion without any help from Jon Arryn. His only real contribution seems to be keeping Dorne at peace after Robert's accession but then again, we can say that it was only because Doran plays to win, not because Arryn gave him any hopes for justice. Securing Cersei Lannister's hand for Robert can be considered an achievement as this marital alliance was the steel that kept the Seven Kingdoms together but then again, it's not like securing the proposal took a lot of effort, we all know Tywin always wanted Cersei to become the Queen.
As for the plentiful years, It seems like Petyr Baelish is to be praised/blamed for that. Petyr Baelish emptied the treasury that Aerys had left overflowing, although he blames the Hand and the King for that. Of course, Petyr's own aptitude for finance kept the economy floating on the surface even though Crown was drowning in domestic and foreign debts.
So the question is, is there any definite proof that Jon was a capable Hand? If yes, what were his achievements?