You can feel it in the first sentence. The message is polite, complete, and slightly too pleased with its own structure. There is a "hope this finds you well," a recap of things the reader already knows, and an ask buried under "any thoughts would be appreciated." It is competent. It is also obviously not a person talking to a person.
The usual repair is a tone pass: warmer, more casual, fewer em dashes. That is rearranging the furniture in a room nobody wanted to enter. The reader is not objecting to punctuation. They are objecting to being handed work the sender refused to finish.
A bot sound is usually a missing decision
A model will happily write both sides of an argument and then ask you to "weigh in." A person who has decided something writes a shorter letter. They name the pick they want, or the one they are leaning toward, and they say what happens if the answer is no.
Respect the reader's time starts there. One question. Enough context for someone who was not in your session. No tour of options you already rejected, unless they need that rejection to choose. A dumped draft includes everything because the model cannot tell what you already know you will not send.
The note is where a human shows up
The brief can be structured. The note should not be a second brief. It is the sentence only you would write: the lean, the apology, the "I will call the vendor if you pick B." If you leave the assistant's note untouched, you approved a draft. That is allowed, and it will read like a draft. If you want it to sound like you, change it.
Approval before send is the moment that becomes possible. You see what they will see. You cut the throat-clearing. You write the one line that is yours. The labels will say so.
Do not ask the model to "make it sound more human" as a substitute for that edit. That prompt produces a different costume over the same shapeless ask.
Write for a cold reader, not for the chat
The session knows the joke, the nickname, the third option you hate. The recipient does not. Writing for a cold reader means expanding the shorthand and dropping the aside. A message that assumes the chat is how you get the uncanny valley: familiar to you, alien to them, confident the whole way down.
They may have no assistant at all. They may open this on a phone, on Monday, in eight minutes they do not have. If the ask is not visible without the session, it will not get answered. It will get a "looks good" or a silence, which is the bot-sound's real cost — not embarrassment, but a wasted turn.
A short test before you confirm
Read only the note and the ask. If a person you respect would send those two lines, send them. If you need the rest of the package to explain why this is a reasonable request, the brief is still doing the model's favourite thing: postponing the decision into more prose.
Cut until the ask can stand. Then confirm. That is how a message written with an assistant stops reading as a message written by one.