I would do A and C.
How is Sherlock's going to know to either train John better or find someone better if people don't let them know.
But since you don't have anything tying you to Sherlocks, and you liked your interaction with Gregory's, I'd try with them.
DH and I went through something similar when we listed our property years and years ago, but we had already signed a listing agreement with the agency. So we had no choice but to go with option A and they took it very seriously and assigned a new and MUCH better agent that treated us better and did a fine job selling the house.
In your situation, if you feel like giving them another chance, or even as a courtesy, I would try to contact the new branch manager and relate what you did in your op. But I also think you're fine if you are in a hurry and just want to move along and work with an agent and agency you feel more comfortable with.
In either case, though, I definitely think a detailed list of what you're looking for is a great idea. I did something similar, and included a list of "must haves" (i.e. house MUST have formal dining room; otherwise, don't show it to us) and "dealbreakers" (i.e. house must have six foot privacy fence around back yard or must be allowed by HOA CC&R's or we won't buy it. Period.)
The agent STILL tried to show us properties that violated the list, though; but after twice declining to see such properties she finally got the hint...and we found something we really liked!
I hope this helps and wish you great success & happiness with your home sale and purchase!