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[ASoIaF] How good was Kevan Lannister as Hand of the King?
gpt
He was able to placate the Tyrells by naming Lords Tyrell, Rowan,  and Tarly to the Small Council, and he appeased the Faith by having Cersei perform the walk of shame, temporarily stabilizing the tensions in the capital. He is the first to take the threat of Aegon, Connington, and the Golden Company seriously, ordering the Tyrells to march south to retake the Stormlands (though Mace will not march until after Margaery's trial). He also sends his father-in-law Harys Swyft to Braavos to negotiate the Crown's debt to the Iron Bank. He was going to resort to paying the debt out of the Lannister pocket if he couldn't raise money elsewhere and if the Bank wouldn't give him further extensions. 

  
So he was doing a pretty fine job of fixing Cersei's mess. Even if Stannis takes Winterfell and Aegon recruits Dorne to his cause, the Lannisters can hold the Crown as long as: 

1. The alliance with the Reach stands. The Lannister-Tyrell coalition still have the numbers and resources to overpower the rest of the continent, especially since the rebelling houses are not united (until Dany arrives with dragons). 

2. The High Sparrow doesn't condemn Tommen and Myrcella as bastards born of incest.