Good stuff ~
I'm still not completely clear about what you are and are not asking. But I'll try.
The story about briskets:
A packer cut beef brisket is really two muscles. As a cut of beef, they're called point and flat. The point is also called the deckle.
The point has significantly more fat in it -- which can be but isn't always marbling. Usually it includes big pieces of fat. As panini said, the flat is usually preferred for most purposes because it's leaner.
The flat is the muscle which does most of the breathing. Even wagyu, CAB, etc., animals' briskets get a lot of exercise. That means they need special care to get them tender enough to be pleasant. Most people think "low and slow" is the only way to go about it, but plenty of guys -- including succesful circuit competitors -- go "hot and fast."
I've experimented with starting on the low side of low. around 225, and bumped to the low side of hot, around 275, to help limit the stall. It works, but I feel you get a better product by using a relatively steady temp.
Barbecued brisket must be cooked "beyond well done and into tender." When raw meat proteins get hit by heat, they contract and twist, but if you keep cooking them under the right conditions, they relax again (called denaturing). Usually that means an internal temp over 190 and a long rest. In addition, some proteins -- collagens -- melt when taken beyond a certain internal under the right conditions, and sort of "baste" the meat internally. The denaturing process accounts for why a piece of meat as seemingly lean as a brisket can be made moist, tender and rich.
The advantage to trimming down to the meat is seasoned bark on both sides. That is, except where the point and flat shield one another -- but there's not much you can do about that.
You have a range of trim options. Some people believe a healthy fat cap helps keep the brisket moist. There's no agreement whether the brisket should be cooked with the cap up, down or flipped part of the way through. In my opinion, very little to no fat is the right amount. You can trim right down to the meat and still get a juicy brisket if you do some other things -- the most important of which are:
- MEAT MATTERS. The meat's quality matters -- a great deal. I'm not saying you can't make a juicy, tasty and tender brisket from a cheap piece of meat. But everything else being equal, a better piece of meat will give you a better result. Every time. Important brisket comps are won with BTC, CAB, Prime and Wagyu. Average rolled Choice doesn't usually show well, at least not comparatively. A 17# brisket usually indicates a large and older animal, possibly not a steer, and most likely a bad choice from the giddyup. And yes, we can stipulate the choice was the client's.
- DON'T CUT PIECES. Briskets cook better as a single piece, not cut in pieces. It's generally a mistake to do any butchering beyond trimming. If you must cut, keep your pieces as large as possible. Larger makes the denaturing process work better and more evenly.
- INJECT. It makes things so much easier and better, I have to question why someone would not inject. That doesn't mean there aren't legitimate reasons not to, but they're thin on the ground.
- FIRE MANAGEMENT. Don't allow too much variance. Brisket is not forgiving.
- NO PEEKING. Keep the pit closed through all but the last part of the cook. That includes not checking on appearance and not mopping. You already know this.
- WRAP. Wrap when the brisket hits the stall. Include some moisture in the package. Yes, this will soften the bark a little, but you can bring it most of the way back by unwrapping. I don't wrap the brisket loose, I use a sheet pan with a donut screen, with a mix of wine, stock and seasoning under the screen, and wrap the pan. Some people -- including (fwiw) Myron Mixon -- use a hotel pan with a steamer insert. Back in the day, old-fashioned pitmasters (including me) used to say: "wrapping is braising and braising ain't barbecue." Whether there's any truth to the statement, you get a much better brisket if you wrap. Remember what I said about "right conditions" when I was talking about the denaturing process? That's where wrapping comes in.
- UNWRAP. Try and time the last 45 to 60 minutes and finish cooking unwrapped. This will help restore some texture to the bark. You can lower the heat if necessary. If you feel compelled to mop, that's the time.
- HOLD. Brisket requires a long rest. It's part of the denaturing process, and a couple of hours is a reasonable minimum. You can hold longer without hurting it. I hold in a cooler, wrapped in cling wrap. This does soften the bark a little, but that's a small price to pay for the good it does for the brisket's interior.
Tight trim or not, you should do all of these.
Equipment can make a lot of difference. ECB's are notoriously difficult to manage, somehow managing to combine overall draftiness with a poorly ventilated fire pan. Additionally, their thin steel shells provide very little insulation and are very sensitive to weather. The most common ECB mod is not to wrap any part of the pit, but to drill out the fire pan so it breathes better. I know the ECB wasn't yours, but a lot of people do use them and they might as well have the information.
A word to Panini: Making your own pit out of whatever and making it work is "puttering," of the highest order, a thing respected by all men especially those of us of a certain age. I salute you. Buying an ECB is just a tragic mistake.
After the brisket is rested, the muscles can be separated and should be further portioned into pieces which are easily managed for slicing.
You can do a lot to compensate for a lot of brisket faults by how you slice and dip. If the brisket is tough, slice it very, very thin -- 1/8" if you can manage. If it's overdone and wants to fall apart, slice it thick -- about 1/2".
Make something like a butter-finished "au jus." If the brisket's dry use it generously to moisten the slices. If the brisket's nicely moist, use it sparingly to get a shine on the meat. FWIW, my dip and injection are usually one and the same; and usually a mix of beef stock, red wine, Worcestershire with some fairly mild seasoning (including thyme, fresh onion and fresh garlic) reduced, sieved, and butter finished. The idea is to lubricate the beef while making it taste more like what it is. It's not "barbecue sauce." A tomato based barbecue sauce is expected in most parts of the country, and should be served on the side or ladled on at the diner's request.
Given that it was a bunk piece of meat to begin with and a bunk cooker, I'm not sure I would have taken the commission without a lot of caveats and a good deal of pessimism. There's only so much you can do.
This takes us back to the original brisket questions. Ice, what happened with yours to make you start asking? It couldn't have been an unalloyed triumph.