You're right, all the boycotting in the world really isn't gonna change a thing. Whatever method corporations find to be the most profitable that's what they're gonna implement, and if they have to exploit, murder and lie about it then so be it. Capitalism has always been the root of the problem and eradicating it is the only solution - to everything. People who think they're gonna change the world for the better by not eating chocolate really don't understand the reality of the situation.
With that being said, taking on the apathetic stance of 'omg boycotting makes no difference anyways' isn't quite the right path to follow either. For one reason and one reason alone. Regardless of the outcome of a collective effort, you are still accountable for your actions as an individual. If Islam says you can't buy something that was attained by haram means then you have to find a halal alternative. In this case the outcome of your actions are completely irrelevant, the only thing that matters is whether what you are doing is halal or haram.
I'm not going to generalize, cause I don't think you really can. There are a lot of factors and I think you would have to look at each company on a case by case basis. For example if Nike has a horrendous human rights history then why can't you just buy a different brand? As Muslims the fashion statement you're trying to make to hide your insecurities shouldn't be more important than following your religious values. And if every shoe company in the world is sweatshopped then go with the least worse one (if you consider shoes necessary to life). Or make your own, or don't wear shoes. You might be suprised to find how many alternatives there are if you look around, but yes that does mean putting in some effort.
Boycotts can be effective to raise awareness to others about the potential haramness of a certain product, and it can also be a wonderful test to see whether Islam or corporate whoredom is more important to you. You gotta be willing to make sacrifices no matter how brainwashed you are into thinking materialism will somehow make you happy.
So the only question to ask is, is the product halal or haram? That's the only criteria to base your decision on.