Many of the men in GoT who are closely involved in the power struggle are indeed quite rational. They have to be, since the less rational tend not to survive for long in that story.
I can't say the same for the women, though. Most of the major female characters in GoT have a streak of crazy in them. Dany, Cersei, Lysa, Lady Stoneheart... The Tyrells seem to be the only exception.
Tywin sends armies to torture villages looking for the brotherhood and burns crops despite knowing this is the last harvest before winter and food stocks are low. Most of the leaders in the war of five kings do the same thing - and get themselves killed to boot.
We only see Lady Stoneheart kill perhaps half a dozen senior enemy commanders.
Tywin burns crops because he wants the riverlands to starve. He is willing to destroy a large swath of the country in order to stay in power. It's a perfectly rational means to a despicable goal.
