I don't think it's that the Autobots did nothing at all so much as the feeling that there wasn't much the Autobots did that the humans couldn't have done on their own. There just isn't that feeling of only one person can stop the bad guy like in something like the Dark Knight. The Joker isn't bullet proof and at one point the police even capture the Joker so the police don't feel completely useless or helpless in the film. But when it comes down to stopping the Joker it feels like Batman is the only person who can. Or Aliens, it feels like the Marines put up one hell of a fight but it feels like only Ripply can stop the alien queen. It almost feels like the humans are the source of almost limitless power and the Cyertronians are the weak species. Even the plot of Dark of the Moon seemed to say the robots were too weak to rebuild their own planet but the humans were powerful enough to rebuild a planet.
It wasn't really a matter of them being "weak" or anything, it was all about resources. Human resources, and the sheer number of them. Cybertronians didn't really have the sheer numbers or resources to rebuild Cybertron, hence why they wanted to "harvest" Earth. Even mighty aliens like Transformers could use the help of several billion human salves. The Decepticons needed a massive slave labor force, if anything, just to haul equipment and drive trucks. The 'Cons were basically saying "We view you as pathetic insects, so be our slaves". I completely agree about the rest of your post though.
You know, I find it more plausible that ants can rebuilt Gingerchris' shed than humans can rebuild Cybertron, most likely due to the sheer unrelenting bad-ass building creed of those lil' critters
They basicly lifted the whole human slaves thing and the autobots leaving the Earth on a rocket from the g1 episodes "megatron's master plan" and then spacebridgeing cybertron was from "the ultimate doom" and that had its share of human slaves as well. At any rate I think the movie autobots are very useful at certain things, killing decepticons in flashy super violent ways and engineering unbelievable super science plot devices. Its just that fans want them to be characters and normal movie people want them to be Alien Automatons. There always has to be a human element, but perhaps the humans had far to much to do in this trilogy.
I mean bad dialogue in terms of the way it is stated, essentially; Optimus and the Autobots knew they were going to fake their deaths and purposefully decided not to return until the mass slaughter of hundreds if not thousands or millions of people in Chicago - it seemed a bit of a douche move by Optimus and the Autobots. There are really only a few ways you can view Optimus's line and the reason why (Despite returning to Earth) they did nothing other than wait for the Chicago attack; Optimus and the Autobots did not return as they wanted to get all the decepticons out in the open - meaning they idly sat by as the Decepticons slaughtered tons of people in Chicago Optimus and the Autobots did not return as they wanted to prove that the humans needed them - meaning they idly sat by as the Decepticons slaughtered tons of people in Chicago Optimus and the Autobots chose not to intervene with the attack on Chicago - meaning they idly sat by as the Decepticons slaughtered tons of people in Chicago