Paid 7,400 to an agent who wrote one contract on a house I found myself

The argument you made was always going to lose, and it's worth being precise about why, because the lesson isn't "agents are sharks."

Exclusive right to represent means the fee is owed on any purchase of the described property type in the described area during the term, whoever found it. That's the entire point of the word exclusive. Procuring cause fights are between two brokers over one commission. They're not a defense a buyer gets to raise against their own agreement. Your prior contact with the seller in December would only have mattered if it was written into the agreement as an exclusion, which is exactly what you concluded.

So the number that hurt you was set in January in three blanks. Term length, described area, and excluded properties. You can shorten the term to 45 or 60 days and re-sign, which costs nothing and gives you a natural review point. You can narrow the area to towns instead of a region. And you can attach a schedule of known sellers and addresses at signing.

One more thing on the 2%: a percentage fee on an off-market private sale with no listing broker doesn't track the work at all, and that's the case where a flat fee is easiest to argue for. 7,400 for contract drafting and coordination is a number you could have proposed as 2,500 in January and probably gotten. Nobody was going to volunteer that.

I'd have paid the 7,400 without much complaint honestly. What I hear in your post is that you'd rather have the roof, which is fair, but the version of this where you write your own purchase contract on a 370k house to save two percent is not a version I'd want either.