I think why everyone hates the German and American UUs and UBs are because they come so late in the game.
I would take an assembly plant over stock factory, but its value-over-base combined with its late-game aspect still makes it one of if not the worst UBs in the game.
Shaving that amount of hammers in the late game is not terribly impressive. Given how things snowball and the fact that coal is not GUARANTEED, the average expected return from hammer savings from buildings like the zig or sac altar are probably better...but that's not even the primary draw of either!
For production, you do not want to be running engineer specs unless your land is pretty bad or you have a HUGE city (which is not super practical for most of the game)
We're talking what, turn 200+, probably 250+ for most people until you see any benefit from assembly plant at all, and when we do see it the usefulness is marginal. I often hate on buildings like the feitoria, but even that thing is better than the assembly plant :/.
Dun is more volatile. In situations where it helps, it could well help a lot (guerrilla II instead of CG I or G I on border hill cities vs early aggression wouldn't hurt, and slapping it on gunpowder later isn't useless), while in other games it won't give you ANYTHING. Then again, even UBs buildings like the dike, cothon, citadel, and research institute can be 100% useless depending on the map/how the game goes, so what we're really looking at here is average expected returns.
We're also a lot more interested in returns that happen before the game is decided. The assembly plant has a decent chance of having the game decided before it is available, and even when that is not the case the returns are so marginal that it's doubtful it has a significant impact on the outcome.
Most Civ players, at least the ones that post on this subforum, tend to be rushers. That's also why I never play Civ4 online, because it's like Starcraft all over again. "Screw playing the game, I'm gonna zerg rush!"
Zergling rushes in starcraft are 100% valid parts of the game. Elite players and even the tier below that do not lose to traditional zergling rushes, by the way, which is why I get lols from 6-pooling people. Your meta-game asplode, try some adaptation!
More to the civ point, the reason earlier uniques are favored is not solely related to rushes. There is a compounding impact from earlier benefits...and while it's difficult to quantify precisely every player who has any semblance of high-level skill at this game knows its there. Sometimes rushes are the reason to favor early UUs, but UUs that simply guarantee your early survival or UBs that provide material benefits 100's of turns before the woofer UBs you're talking about also fall under the category of "early, compounding advantages".
UB.
