Okay, I've played Tweaked China a bit more, into the Renaissance. I like the concept, but it still feels a bit rough. I will also talk about the 3rd and 4th Uniques, but I will just post it here.
I went Progress, in order to set out a number of cities, to best generate WLTKDs. I played on Epic, Large, and while I ended up on a continent with 4 other civs, I ended up having a decent amount of space, aided by a bit of aggressive forward settling and an early fight with India. I ended up settling 7 cities, in total and conquered 2 off India much later, then vassalised his remaining city, 1 annex, 1 a puppet to stop their pressure (they picked Churches as their first belief, so I wanted to head them off early) from killing my religion. I noticed that conquest of cities with a existing 8 don't seem to give WLTKD, so Authority would be suboptimal with this China.
Of them, only my capital triggered in the ancient era, while all the rest triggered one after the other in the Classic era. The later ones settled in the Classic era I got online quickly with internal trade routes.
I got the first religion with the mine pantheon, lots of mine luxuries and Mt Kalish in my second city. I built the religion around WLTKD, so Theocratic Rule and Synagogues. And grabbed Halicarnassus in my capital.
But the WLTKD, ended up somewhat wasted because the rapid growth just knocked me head-on into a wall of unhappiness. First I had to take Equality before Expertise, which temporarily pulled me out of the unhappiness. But it didn't last long, and soon I was back in the red, despite actively trading for luxuries, targeting happiness buildings, and spreading around trade routes and internal routes. Which then meant I couldn't reach the second trigger with most of my cities. The capital I got to it, and the third trigger, since it was easier to reach with a bunch of settlers having subtracted population.
So by the time I reached Burghers, the string of Classical-Medieval WLTKD had ended, as too had the circuses, WLTKD I had built in my cities for happiness management. Most of my cities were shy of 16 by varying amounts and with the happiness situation, some would take a while to hit the trigger.
As for the rest of the kit, most of it is aimed at a more Tradition playstyle. Paper Maker doesn't offer much of a bonus, a few stray gold and science on great works isn't much for a non Tradition civ, and it being subject to era change makes it even worse. Examination Hall's extra gold on Great works is also negligible. The GPP on citizen birth is a decent concept, but it came after my great growth spurt in the Classic, so I didn't actually get that much from it, with the growth in my cities largely stalled out.
I think that China really needs some extra happiness management, to suit its major growth. Otherwise, the hitting of the population triggers becomes a major struggle, and the food bonuses get wasted.
Also, do the WLTKD number of turns scale to game speed? They individually feel a bit short. This was fine in the Classic era at first, when my cities were hitting 8 population within a few turns of each other, but after that, it felt too short. Not sure if this too is by design or an issue of playing on different game speed. The current length might be okay if the trigger were lower, but the gap between 8 and 16 takes a while.
Examination Hall also comes too late. Historically Wu Zetian, and her changes to the examination system, happened way earlier. It coming earlier allows it to appear in time for the Classic spurt of growth, instead of that coming and going.
Finally, I think that either the Great Work focus needs to be changed since the UA no longer grants WLTKD by creating great works. Both UB give bonuses to them, but going Tradition limits the WLTKD. Generally, the design of China feels a bit too spread out. Parts of the kit urge going Tradition, others Progress. Then there is Artistry (Great Works), Fealty (WLTKD and growth), and Statecraft (City State Influence). Some civs should be all-rounders but tweaked China, with 3rd and 4th Uniques, feels a bit more like playing with a partial kit.