Performance is an issue for everyone, not just folks with "potatoes." Every province added in CK comes with additional characters, all of whom interact with every other character within diplomatic range (if only to check what their opinion of that character is, and whether they want to scheme against them this month). That's a noticeable performance hit. It probably won't cause the game to fail to run except on very old computers, but it will cause some degree of slowdown on all computers. And no, "optimization" is not the answer. There's no magical "optimization" dial that the devs can just turn and make the game go back to running as fast as it used to. "Optimization" is extremely time and labor intensive (you are going through all the code, trying to find minor tweaks that can be done slightly more efficiently) and not costless in terms of effects on the game (one of the easiest ways to optimize is to cut things out, but that's a loss of detail in other areas, no matter how minor: barons in CK2 used to do all sorts of stuff on their own, but after RoI one of the optimization changes to balance out the increased lag essentially cut out all of their individual activities so now they just sit there, marry generated wives after they inherit, and have exactly 2 children).
And as noted, 99% of playthroughs, China won't matter (assuming they don't make it ahistorically powerful and expansionist, which admittedly past Paradox experience with blobs suggests they probably will). Look at India, for a comparison (a region that honestly had much more interaction with the pre-ROI CK area than non-Mongol China did): unless you start in Persia/India/Tibet, you generally don't care what happens in India. It just sits there and does it's own thing, not affecting Europe, Africa or most of in-game Asia at all. China will be the same way (unless they screw up and make it super-blobby, which they probably will). eating up processor cycles without being something that most players notice (because most players will continue the CK approach of generally playing in Europe or one of the areas bordering Europe for most of their games).
More is not necessarily better. Better is better; it may involve more, but it very frequently involves less, but more focused.