Is it not a sort of genius to cut always to the heart?

I'm reading The Song of Achilles by Madeline Miller. Its narrator asks, "But is it not a sort of genius to cut always to the heart?", and I don't quite get what it means.

Considering this is the part you're talking about:

I stopped watching for ridicule, the scorpion's tail hidden in his words. He said what he meant; he was puzzled if you did not. Some people might have mistaken this for simplicity. But is it not a sort of genius to cut always to the heart?

I believe the narrator is trying to say that he has stopped watching for any hidden intent in the words of the person he/she is talking about (presumably Achilles). That he speaks directly, striking at the heart of what he wants to say and does not attempt to beat around the bush or try to get his point across in an indirect manner. Used in a manner similar to "cutting to the chase" in a way.

Quote

I haven't read the book but I searched for the line you are mentioning on goodreads. This is the complete quote:

I stopped watching for ridicule, the scorpion's tail hidden in his words. He said what he meant; he was puzzled if you did not. Some people might have mistaken this for simplicity. But is it not a sort of genius to cut always to the heart?

Piecewise Explanation

I stopped watching for ridicule, the scorpion's tail hidden in his words. He said what he meant; he was puzzled if you did not.

This means that the narrator earlier used to take he's words as a ridicule - comparable to a scorpion's sting. But not anymore. Narrator has understood that he only speaks his mind. He is so simple (naive maybe) that he doesn't know that others don't always do the same.

Some people might have mistaken this for simplicity. But is it not a sort of genius to cut always to the heart?

The narrator explains that while some people think that this behavior can be classified as simplicity, yet as per narrator this behavior is actually the quality of a genius person to speak what you mean and cut away all the fluff from what is really important.

To "cut to the heart of the matter" is an idiom that means "get straight to the point". But "cut to the heart" can also mean to strongly engage someone's emotions, as a song might do.

Which meaning applies would depend on context.