Organ Guns are nowadays Range 30'', 2D6x2 shots. I think total game time was about two and a half hours. That, for three Empire and two Dwarf turns.
I think he didn't fully realize the extent to which Rangers can harass and interfere with movement, he's probably not used to thinking of them that way. He does recognize light cavalry as doing that, probably due to his most common opponent being a Highborn Elf player who uses light cavalry for that role. He usually deploys (quite correctly) his crossbowmen to counter such.
I concur with most of your analysis of what mistakes he made. I don't think though his combat blocks had much other choice than to charge my harassment units, they were placed close enough that going around them would have delayed his advance at least as much. Charged Rangers at least need to spend a turn rallying before they can do it again, unless they happen to rally in a fortunate position.
I think he put his left-flank crossbowmen there to counter maneuvers from my Reiters, but putting them behind the wall was unnecessary and suboptimal. There wasn't really anything seriously threatening them anyway over there that the wall would have made a difference against. With the Deep Watch and the Warriors side by side, it would have been harder for me to pincer off the Deep Watch.
I suspect a common cognitive flaw is to be stuck in thinking what a unit is ordinarily supposed to do, rather than what it can do under present circumstances. Like he put his crossbowmen behind that wall and his Organ Guns on the hill, positions that are usually advantageous for that kind of units, but might not be the best under present tactical circumstances. His plan might have worked if the crossbowmen had been on the outside the left-flank pincer arm, and one of the organ guns on the inside of it. To cling to a particular formation, as you mentioned, would be another example of this. By sending my halberdiers on that long march, I essentially broke up my own trademark formation. The same thing goes for shooting units, particularly the less mobile ones like handgunners and crossbowmen. You may feel like you "should" shoot with them whenever they have a target in their sights because "that's what they're supposed to do", even though situationally they might be more valuable doing the job of melee detachments.
I did commit my share of gambles though, that could have failed. The halberdiers could have panicked. Failure to snipe the Vengeance Seeker would have enabled the little git to block the maneuver, and cost my leftmost crossbowmen time they could have used to turn to face the left-flank pincer arm. Still, things went overall so swimmingly that I could have failed and still had a fairly good position left. Whatever happens on the left flank, I would probably have bagged the right flank by the Demigrpyhs sweeping away his warriors, followed by shooting up his deathstar so badly that I could have wiped it out with a combined charge of Imperial Guard, Halberdiers and Demigryphs, all before the left pincer arm manages to interfere.
Zygmund, I have to say, your stated aversion to a gaming scene where the players have an analytical attitude about the game surprises me. You seem to me more analytical than most