Sorry to hear that. Smoking something that small is tricky, but I thought with the point you had a good chance of it coming out okay. I guess our lesson is save it for stew at that size. 
That’s how hot my WSM runs, and that’s how I like my cue, cooked a bit hotter. I’ll even do something like pork shoulder without the water pan (well, mine is filled with sand) to get that fat-in-the-fire flavor.
Before I try this again I want to know if I’m setting myself up for failure or just missing something important.
Well I was going for a BBQ, not a roast.
A pot roast simmers in liquid for hours to reach that temperature, and I thought the time it took to reach it (low and slow) was a factor in breaking down the meat, not just “reaching 200F meat temp”, I would think the same is true of a smoke/grill method as well?
I see in that YT clip of the guy who made a “small” brisket (7 lbs., LOL) in “just” three hours was also spritzing it multiple times, I never did that… I had a pan of water under the meat in my grill but that’s all. (And maybe not enough water?)
And I had rubbed and then marinated the meat, and put it on my grill wet - evidently the “crust” or “bark” is supposed to form as an interaction of the rub and the smoke, so no marinating at all then? (This guy didn’t.)
And finally I didn’t put my smoke box of wood chips in directly over the one burner I had on, like I had it balanced cross-wise (almost perpendicular to the burner), which only burned the chips in a small area of the box. I had to rotate it to nestle fully against the fire to produce significant smoke, that was definitely a problem.
I’m willing to try again with a single small “pot roast sized” brisket as an experiment…
Hmm, maybe this recipe could serve as a guide for a 3-4 lb. cut?
And, if I smoked two 3.5 “roasts” next to each other, they should cook at the same time right? (It wouldn’t be like making a single 7-8 lb. brisket/roast?)
You can overcook brisket to the point that it dries out. It’s less forgiving than pulled pork. I used to cook brisket flats in a smoker along with big cuts of pork butt, and by the time the pork was up to temp the brisket flats were practically brisket jerky. They were still tasty, but not the wiggly, juicy deliciousness that perfectly BBQed brisket should be.
The temp isn’t the only thing to go by. I’ve had pork shoulder finish and pull as low as 195. You kind of have to have a sense of what should look and feel like when it’s done. I’m not surprised by you having issues with the flat, but with the point I would expect much more forgiveness.
Yes, and @bump is right that ‘low and slow’ doesn’t have to be all that low. I usually go around 275F because I have trouble getting my smoker to go much less than that without killing the coals. I use sand for a heat sink instead of water, which would probably help cool things down more. But I get excellent results at 275. A sustained temp of 300 seems like it would be a bit too high, though.
The technique sounds pretty similar to what we’ve given you here, omitting the last hour finish unwrapped on the smoker, so it’s worth a try. The unwrapped portion of the smoke after wrapping is to dry out and crisp up the bark again, but maybe even just an hour is too much and dries it out too much for a piece this small. I sweat, though, that’s exactly what I’ve done with a chuck roast, but that was like fifteen years ago.
You marinated it? With what?
Per the recipe I initially found in my OP - overnight in red wine vinegar, garlic, etc.
I used a different mix of spices based on what I had handy, but that was the main ingredient of the marinade.
I don’t know if that affected the cook, but I’ve never heard of brisket being marinaded.
Someone linked to amazingribs.com earlier. Their how-to on brisket is required reading for anyone working their way through smoking a brisket, it’s an amazing, well-researched resource.