It is a near certainty that the listing agreement that the listing agent has does not give the seller a discount if the buyer is unrepresented. Nearly all listing agreements are written such that the seller pays a commission which the listing agent can share with a buyer's agent. A buyer being unrepresented does not change the seller's obligation of commission at all. Your offer of being unrepresented is not likely saving the seller any money at all. You think it is because you don't think it is fair that the listing agent can get it all if you are unrepresented, but that is just not how listing agreements are commonly written. Yes I am making an assumption of how his listing is worded, so I could be wrong. But I can't remember the last time I saw a listing agreement that wasn't worded the way I explained. And if it is worded as I have explained you are actually asking the listing agent to accept a lower fee because he isn't sharing with a buyer's agent. That is something he is not likely to do.

If buyer's really expect to get a discount for not having an agent then you likely need to find a property that is not listed.

All of that said. It is a scummy move to send back an offer written as him representing you for 2%. He definitely should not have done that. If it were me I would just make clear that your offer is submitted but I would explain that it isn't actually a "better deal" for the seller because the commission outlined in the listing agreement doesn't change based on if the buyer is represented or not.