It depends how unit preservation has been going on both sides. If the US players have managed to stockpile like six tanks, it's possible to just steamroll everything at around this point.
But, since the title of the thread is "comebacks", I assume that you mean you're already a little behind. In that case, it's very difficult but if you double team one area of the map it can be done.
Of course you will fight harder opponents as you rank up. That's the whole point.
It's easy to blame losses on imbalance, or 'cheese', but if you want to reach higher ranks you have to change your attitude and look for ways that you can improve. Your losses are your biggest learning opportunities.
I can assure you that 'blobbing' will not work against proper counters. As USF, I have almost never lost a game due to truck pushing, camping, or snipers.
All of the things you've listed here are counterable. It's simply a matter of improving your skills.
Making a public mockery of people who rage and throw accusations is against the site rules. Am I the only person getting tired of seeing these threads every day?
Besides, getting called a hacker doesn't justify calling your opponent an idiot or a moron.
I have a 3770K @ 4.4Ghz, a GTX 780, 8GB of ram and I max this game out on 2560X1440. Just put AA at low (any higher wont net any visible improvement but will lower performance) and game resolution at 100% and max everything else. I'm not sure how people with higher specs than me are having issues...