A tidy 20 year old CG 125 will be better than new Chinese junk some motors are based on Jap bikes but the innards are made of chocolate and the fasteners are hilarious after a winter.
The comments about the internals is certainly true in my experience. I tried to install Suzuki parts into the k175fmi engine that it is cloned from. However, the valve guides are narrower, so you end up with very weak valves and smaller parts like valve colletts/etc are very hard to get.
There are things like replacement heads available, but they have no internals. So you have to either reuse parts or go hunting for 3rd party bits to replace them with.
My engine had dropped both valves before 12000 miles at different times.
My bike was 5 years old, and most fasteners were ok, but some random parts were letting go.
Rear brake master cylinder, brake cables, needed changing, the frame had surface rust all over and had to be stripped and cleaned, brake caliper taken back and resprayed. Most of the plastics had some broken clips or looked worse for wear.
Some metal parts like the rear wheel/chain adjustment were actually falling to bits and needed total replacement.
So when you compare it to my 1960s Honda it's faired pretty badly. That bike has most of its original parts and others could be re-worked to be reused.
I went into Chinese bike ownership with my eyes and mind open, and sadly a lot of the prevailing wisdom and advice from other bikers turned out to be correct.
Chinese bikes are moving on, and maybe the current generation will present a step forward again from my 2013 bike, but based on my experience, they have long way to go.