It's not out of the question that a China that continued to emphasize naval + exploration (and maybe had some contact with Ottomans/Portuguese as a result) could manage legit war-capable ships, however. They certainly had the means produce such ships, and could probably source foreign experts from nations aligned with them if they really wanted.
But the game doesn't model any of this in the first place, so it's unreasonable to slap players/nations with the restrictions as if this is a choice they actually made. Same goes for tech penalties absent institution management, actually.
Almost certainly not. Even in the 16th century captured Ottoman naval guns were viewed as so inferior that the Venetians melted them down and then had to add refinements to re-alloy and recast them as something useful. Chinese metallurgy would have needed massive upstream improvements to come close to getting the quality needed for naval guns that would not make the ship too top heavy. And a lot of those innovations required things that China was drastically short on (e.g. large scale forestry operations, charcoal).
Likewise, prows would be a major issue. For most of game period the Europeans were pretty unique in having large scale, well husbanded forests that made fast oceanic shipbuilding possible. Prows and other key bends in the ship were normally made by finding trees with the correct bends growing in low density forest. Scrub forest tends to be too twisty and the grain too uneven to be strong enough. Old growth forest has too little sunlight reaching the lower layers so the overwhelming majority of the trees are ramrod straight and not prone to bending back. To get European style shipbuilding China needs not just shipwrights, but carpenters, foresters and decades of forestry management. The treasure ships were an extremely good design given where and how China was sourcing their timber, but they are never going to be fast enough to compete with European warships.
Because reality is, the Chinese were not dumb. Lots of countries tried to replicate European successes at sea and with artillery. But they needed not the thin skim of technological progress at the top, but the deep layers underneath to have a prayer of doing it. There is a reason why Ottoman attempts to build Western European style ships in the Indian Ocean failed. There is a reason that Koxinga's ships suffered massive losses to just the
Hector, which they got lucky when it exploded to either a freak shot (cannon ball hitting a high angle and falling down into the gunport) or a misfire on the
Hector setting off the powder store directly. There is a reason why all the Mahgreb states stopped casting their own cannons and just started buying British.
And I think ultimately, the bigger deal was that many of the competing loci of population peaked long before Western Europe and depleted their transition resources long before the Europeans did. China had massive population density for forever and they basically eliminated all of the large-scale forests within China centuries before game start. Likewise, Europe was weirdly attached to animal power and most of the rest of the world had had it severely culled to feed the population at some population bottleneck (e.g. Tamerlane) which resulted in a lot of weird technological implications (e.g. tallow availability allowed the Europeans to do things with leather that could not be done cost effectively elsewhere).
Should the rest of the world be able to develop all this downstream stuff? I guess. But the conditions that lead to it just are not present in the rest of the world and engineering them would be impossible (e.g. mass reliance on animal power is hard in Africa where the horses die whenever they get bit outside). A lot of the technology developed not because it was the best solution overall, but because it made the best use of the currently extant resources and nowhere else has Europe's resource mix (and it often took about a century for the colonial ventures to replicate that resource base).
Now should the rest of the world be able to conquest Europe? Absolutely. It would have been quite possible for the North Africans to consolidate, cut an unholy alliance with France or Aragon and retake a base in southern Iberia and push north (particularly if France later goes Reformed and partitions the places with Sunni allies). And if you are holding Seville, then you should become heir to Seville's technology.
End of the day, the game has the military backwards. The hardest thing to replicate was the navy, not the infantry. The rest of the world should struggle the most with warships, other ships, artillery, galleys, infantry, and cavalry in that order. And it would make the most sense to tie unit recruitment to provinces (or at least cultures) and not to states.
