imo sub-Saharan African countries should never be able to westernize. Which is why I will be making a mod which disables westernization for African tech countries. Why do you think Europeans could draw up African borders with a pen and paper? The African nations were so backwards in comparison to the European powers, you can't deny it - open a history book if your deluded enough to think the Africans had a chance.
I don't know what history books you're opening, but they aren't the same ones I've seen. How many major African states were conquered by Europeans prior to 1800? Mutapa, one of the most remote of all African states in this period and with far less contact (and less technology from) withWestern powers than those around Mali and Ethiopia, survived until 1760. Even then they only collapsed on themselves and were de facto independent of Portugal until the 1900s.
I'm sorry, but your view on Africa in this period is incredibly flawed. There's a reason (a few of them actually) that, historically, African wasn't overrun by Europe until the late 1880s. Malaria aside, and even with their greater technology, Europe completely lacked the manpower to effectively invade Africa en-masse. Heck, the only reason the Americas were colonized so effectively is because 90% of the population died off in a freak holocaust. If that doesn't happen, Europe finds itself having a far more difficult time establishing a foot hold in the Americas. To say that Western powers should just stomp across everything in Africa in the EU time frame isn't remotely accurate to how history played out.
And maybe Mutapa and some of the Swahili states are "too far behind". But Mali? Really? A land that has had regular contact with North Africa and even Europe for over a millenium? The region wasn't as backwards as their placement in the Sub-Saharan group would have you believe and it wasn't populated solely by wandering tribes just now learning the art of tying a pointy rock to the end of a stick. Maybe it should be harder for a Sub-Saharan to westernize (ignoring the fact its harder for a Sub-Saharan to survive to Westernize), but maybe Mali shouldn't be quite as backwards as Sofala to begin with.
But from a gameplay standpoint... do we really need to make even easier for Western tech nations? Mali actually becoming realistically resilient to European efforts at conquest seems silly when on the opposite side of things its ridiculously easy to overrun all of Asia with a Western nation. Again, there's a reason you'll see empires in the "post my empire thread" where they've painted all of China and India but abruptly stopped around Anatolia.