I wouldn't say the game is garbage, it's a solid follow up to the original and with patches, most things will get even better. Big problems are the DLC, bulletin and online system and the idea of marketing/producing CoH2 towards the comp stomping/casual community. There are plenty more problems that have made the game unfun to play to the point where I just don't feel like playing any more and likely won't.
If eventually there are patches in future that improve CoH2 to the point where it's fun enough then I'll play it again, but I don't have to force myself to play it, I'll just wait until that time.
First off I am not a pro, but here is my opinion. Yes I agree with you that the DLC is the main problem. I think the best way to get what we want from Relic/Sega is not by you not playing, but is by you not "paying".
The bottomline is that they have your money and they aren't going to get give it back. If Relic knows that you are not happy and not going to pay them more money in the future, they might make changes. So, I think the best way is to not buy their "new content" and tell them that.
I think that we are correct to voice your displeasure and tell/show them why you won't pay them again until they fix the problems(imbalance/new content/lack of support/lack features/ALL of what HolyHammer said

).
However, from the state that COH2 is in and the way it is going I don't think it can be fixed. How can it when every time a patch is release where they fix an imbalance, but they release new content with the changes that wasn't in the previous problem? It is counter productive because if you balance the game by buffing/nerfing a unit say the T70, how can it balance if it hasn't been
properly play tested against a new unit/ability? IE: Soviet Industry? Now Relic has to go back and makes changes again and perhaps undo some changes that they did before which is what I meant by counterproductive.
But hey.... this is just my opinion and to be frank, I don't think there will be a good RTS for a long time. As nowadays it is all about money. Think about it, would you make a RTS, spend x hours developing, support, play testing, etc... and make an one time sale?
OR
Would you rather do all of the same things I have just mention and say... make a MMORPG and have people pay you every month? Or perhaps have them pay every month for a new commanders and "new content"?
Money/Math rules here.
So, what does leave us as the RTS community? Well unless a company goal is to make a RTS and make a one time profit from it(which by the way wouldn't be a very good business decision) then we would rarely, if ever see a good/balance RTS again.