Originally posted by Col. Valerian
'I don't know why I'm even bothering with you' honestly seems like it goes beyond that statement. I've never treated you badly tbh.And not idiotic. Whenever Vader and Galen fight during TFU and TFUII, Vader never actually attempts to kill him and in the novel is described as not going all out, etc. And Galen, even then, is hard-pressed against him all the time. So, that's why.
The novel STATES that BEFORE that point Vader had either not been giving it his all or Galen himself had acquiesced so Vader at the time also had the advantage of Galen not knowing his full capabilities.
"The apprentice understood that, until this moment, they had never truly fought as equals. His master had either held back or he himself had capitulated."
And Galen still defeats him both in lightsaber combat and in the Force. This is after he's fought through the Imperials standing between him and the Rebel leaders on the Death Star. And even still he retains enough energy to fight Sidious afterwards.
Thus my seemingly "aggressive" response is really me being frustrated with the lack of thought that went into your post.