I really don't understand the argument that "Ming was historically powerful, so they should be powerful", especially when you're basically saying "all the time", because that's what ends up happening, which absolutely isn't true. It would be more accurate to say "Ming was historically powerful, but also extremely decadent and lazy". Historically, Qing was formed in 1636, and finished off Ming in 1644. Aside from the fact that it's basically impossible to do a full conquer of Ming in that many years, that's the middle of the game, with 150+ years left. Jianzhou and all the other hordes have so very little going for them here, and their strength in the game is measured by the amount of provinces, development, and tech they have, which isn't an accurate representation at all, not to mention that they are often conquered by Korea, Ming, or just sit there doing nothing important, like they have zero aspirations with what their cultural strength provides them for so little a time span.
I know it's futile to argue gameplay and history, but we are playing a game based on history, that tries to add a lot of historical references, and definitely tries to steer it in a certain historical direction. This should apply to Ming, in that they should only have 100 years or so of stability before they start getting hammered hard by random events that severely threaten them. That would be an accurate representation of Ming.
Yes, Ming is powerful, but let's not forget that they were also conquered. You will almost never see that as it currently stands... definitely not without player intervention. Nevermind that Ming crosses the world due to "unrealistic logistics" or whatever that was... that part is actually feasible and arguable, assuming historical Ming cared enough to try (which they didn't)... They were easily just as capable of traversing the world like all the major western powers, they just didn't... most probably because they weren't even around when all of that really started taking off. We're basically talking about one of the biggest upheavals during one of the most active periods of our world history... no one knows what they could have accomplished.
A thought I had was perhaps adding a crisis on the end of the Mandate horde disaster... like once it starts ticking down, it's basically a near-game ending time bomb for them that they absolutely have to fix before they are well and truly screwed. I'm thinking that once it hits 0 (in addition to having an active horde disaster, not just having 0 Mandate), they should immediately have an unwinnable civil war that splits all of their northern provinces into independent nations, and moves Ming to its southern provinces... basically forcing them to lose all of their power. I would think it should also remove all of their current armies and money, and instead give them a loyalist stack to help defend in the early years of this separation. That would be a lot more accurate than what we have now. Not only that, but it would also be fun. Something that can easily be avoided, if the player stays on top of it, or something that could be considered a challenge (getting back the Mandate of Heaven for a doomed empire, against a Ming-powerful Qing usurper). An alternate path to this would be having this event tick off once a horde conquers Beijing (which you are basically assuming the horde disaster is active and Mandate is close to 0)... so there will still be a rush to try and beat Ming, but it adds a much more interesting spin on things.