Do you mean that liquid was added half-way through cooking time, or that you kept the pan half-filled with liquid, throughout the whole cooking time?
8-10 hours might be right for using a slow cooker. But for the oven, a 3 to 3-1/2 pound brisket would only take about 3 hours. Also a brisket done in the oven should be tightly covered with a lid or foil.
Here's an oven brisket recipe from this site:
And some tips from Bon Appetit on cooking brisket:
Unfortunately, the amount of liquid you add isn't going to keep a cut of meat from becoming dry and tough. If your particular cut didn't have enough collagen to sustain that long cooking process, the protein structure is going to squeeze every last drop of moisture out of the fibers. If I'm slow cooking meats in the oven, I generally check them every 30 minutes or so (and give them a good spoon baste) and cook only until they just fall apart.
Actually can't explain just why. But in that time the whole cut should be about 180 degrees. That's far more than I like. Check core temperature regularly is my tip. Or make "pulled" brisket. Little higher temp to brake down collagen and cook the h.... hell out of it.
I, too, am curious about what "liquid 1/2 way means." Low and slow are, naturally, the watchwords for any braise, but there is definitely a time limit. I cook professionally, so the briskets I use are enormous compared to those any of us would use at home. Still and all, I first smoke them for about a half hour, then braise them in French hard cider for 5 hours at 225 degrees. I suspect that your braising time is too long and that your liquids should be increased.