I used to hate it. "Plato's Stepchildren" too. Probably more so that one, due to cringe factor.
I've grown to appreciate "Whom Gods Destroy". There are parts that are a little too rich but on the whole, there's a good story idea at the heart of it all.
Plus I like the potential of Garth's madness, as a tragic and comedic figure who can turn on the spot, capable of being truly terrifying. Any story featuring him, needs to show him decades before, and why he's such a respected legend - his exploits as a great explorer, required reading at the Academy. He was out there doing a lot of good, before he became mentally ill. It's only touched on in the dialogue and Kirk's reactions, that of earnest hero worship. Even in an asylum, he's managing to hold court over his own little distorted Federation council.
Heresy to suggest that he's actually more interesting than Khan... but somebody could certainly make a case for it. One is a two-dimensional despot, who only got interesting when on a quest for vengeance. The other had the potential to be more of an equal. The flip side of a Starfleet credit. There but for the grace of god goes James T Kirk...