Isn't heart of darkness the one where China can make more hand made goods and swamps the global economy to make it where you can't build factories? As I been I didn't buy it because I heard that.
This is reminding me why I never played as a European nation before as Great Wars aren't enjoyable because of rebel hell. At least as America I can fight with allies and keep the bulk of my amries on the homefront to deal with rebels. But as Germany I just can't. Its basically get it done before 1870 or your fucked unless you are picking on non-civilized/partly westerned nations.
I've not had that issue ever with Heart of Darkness at all. Not quite sure where you've heard that.
As for your rebel issues, there are a few things that can be done to help. One: let your enemies deal with them. Say, if you're Germany with capital in Berlin, focus on your eastern front and let France battle with any rebels. redirect your forces elsewhere and take out the rebels first that are out of the way.
Another good one is to have an extremely oversized army just for rebel stomping, and to never use it in offensive wars so it will always be available to knock out rebel stacks, especially on critical provinces for warproduction. That way there's no bringing back frontline armies to stomp rebels.
One thing that may help out is if you create a large puppet that is contiguous with your country, and that may provide you with sizable armies. Let's look at a Greater Germany:there are quite a few potential puppets. Switzerland, Venice, Hungary,etc. Having one of those, especially one that is a secondary power, can help. You don't have to bring your alliesto the war, butso long asthey are contiguous to your country they tend to be good at helping with rebels. Though Hungary with all of its borders is a big risk of becoming a Great Power. That happened with my last greater Germany game. In the end, don't call them into the war, and they won't be fighting the troops involved in the war, so they can help you so long as their armies are large enough. Just make sure the vassal isn't to strong to risk Great Power Status.
EDIT:Tomakethat last bit clear... Make a country your puppet. Make sure it is contiguous with you. And then
don't call it into wars, at least not at first. It will help you hunt down rebel armies, and it will also provide your troops safe haven.