One might also argue that Kirk got less timid about using the high-power blue setting as he gained combat experience.
Most of the blue beams were fired in "great anger", against targets that would not have succumbed to less, but absolutely had to. The primitive missiles from "Patterns of Force" and "FtWIHaIHTtS" probably shouldn't have warranted such walloping, though, nor the Tholians in their titular ep.
Timo Saloniemi
Well, it was Spock who fired the phasers in "The Tholian Web." I'm not convinced he would have used some kind of "great anger" setting.
"Set phasers to 'really pissed off!'"