you are right zane yeast tolerance for alcohol does help determine sweetness/dryness. the more tolerant, the more alcohol they will produce. but also amount of sugars to fed on, when they run out of sugar they will stop. aspera is right, in part of the control is getting to a point and stopping the fermentation. residual sugar contributes to sweetness. there was a couple of things in your post i was wondering about.
The recipe called for 12 pounds of honey, nutrient, and "up to 5 gallons of water". The dry yeast is Cote des Blancs.
I dissolved the honey into 1 gallon of hot water and added the remainder of water until I hit the 6 gallon line
12# of honey and 4 gals. of water should have made the 5 gals. (14# of honey avg. 1 gallon) if you added another gal. of water you diluted your must that much more. most of my experimental batches are 5 gal. i use a 6 gal. carboy to give head space at the shoulder. i do adjust the sg to go over 5 gal.. that way when i rack to a 5 gallon carbouy the head space will be less. with later racking, i add campden tablet to stop fermentation and add water and/or honey to flavor and adjust space. have you got "mad about mead"?
"Any fool can learn, the trick is to understand - Einstein"