Literature: Separating the text into verses obscures Moroni’s intended contrast. It should read: “… but thou hast not made us mighty in writing; for thou hast made all this people that they could speak much, because of the Holy Ghost which thou hast given them; And thou hast made us that we could write but little, because of the awkwardness of our hands.” Moroni contrasts his and Mormon’s writing unfavorably with their speaking ability. Moroni, while speaking, can feel the electric communication that accompanies teaching when the Holy Ghost is present and enhances human abilities. In writing, the audience is distant, and that powerful two-way communication is missing. The awkwardness in writing that he notes results from the audience’s missing spiritual feedback.
By commenting on the brother of Jared’s “mighty… writing,” Moroni is surely referring to the brother of Jared’s record of his experience with Yahweh and vision of the world.
Reference: The contrast between being mighty in speaking but not writing also appears in 2 Nephi 33:1: “And now I, Nephi, cannot write all the things which were taught among my people; neither am I mighty in writing, like unto speaking; for when a man speaketh by the power of the Holy Ghost the power of the Holy Ghost carrieth it unto the hearts of the children of men.”
The antithetical contrast of being mighty in writing but not speaking is in 2 Nephi, but in probable reference to Joseph Smith: “And the Lord hath said: I will raise up a Moses; and I will give power unto him in a rod; and I will give judgment unto him in writing. Yet I will not loose his tongue, that he shall speak much, for I will not make him mighty in speaking” (2 Ne. 3:17).
I suggest in the commentary accompanying Moroni 10:28 that Moroni has used language he gleaned from the small plates. I believe that this is the case here as well. I believe that Moroni read, was impressed by and identified with, this contrast between writing and speaking. He echoes that language here.