turtle-paced Answer:
From Oldtown to the Wall, men began to say that Aerys might wear the crown, but it was Tywin Lannister who ruled the realm.
It was Tywin Lannister who settled the crown’s dispute with the Braavosi (though without “making the Titan kneel,” to the king’s displeasure), by repaying the monies lent to Jaehaerys II with gold from Casterly Rock, thereby taking the debts upon himself. Tywin won the approbation of many great lords by repealing what remained of the laws Aegon V had enacted to curb their powers. Tywin reduced tariffs and taxes on shipping going in and out of the cities of King’s Landing, Lannisport, and Oldtown, winning the support of many wealthy merchants. Tywin built new roads and repaired old ones, held many splendid tournaments about the realm to the delight of knights and commons both, cultivated trade with the Free Cities, and sternly punished bakers found guilty of adding sawdust to their bread and butchers selling horsemeat as beef. In all these efforts he was greatly aided by Grand Maester Pycelle, whose accounts of the reign of Aerys II give us our best portrait of these times.
Yet despite these accomplishments, Tywin Lannister was little loved. His rivals charged that he was humorless, unforgiving, unbending, proud, and cruel. His lords bannermen respected him and followed him loyally in war and peace, but none could truly be named his friends.
The World of Ice and Fire, Aerys II
First, always remember that this is an in-universe history text that makes absolutely no secret of its partiality or agenda. It was meant to be given to a ruler in universe, first one who’d married a Lannister, then one who’d descended from a Lannister. (More than one Lannister, as it turns out.)
Next, even presented in this favourable light, these developments are generally favourable to those who are already wealthy and powerful. Trickle down principles are firmly in effect. The best thing here, I think, are the roads.
It’s that last paragraph that I think is the key. Tywin’s character. The nature of the government means that character and politics are intertwined. There are no checks and balances to stop personal cruelty and an unforgiving nature affecting the policy of the realm. Even a favourable account cannot entirely gloss over the sort of person Tywin was and the effect it had on personal politics.
