Regarding the problems of weather avoidance in the PRC - I have been flying into and out of China for almost 25 years, almost every time I strap into an aircraft. I have done thousands of weather deviations there over the years. Requesting weather deviation is the same as anywhere else in the world. Whether you want 5 miles or 50 miles deviation, just tell them what you need and you will usually get it.
However, it is not unusual to have deviation refused due to military activity, or proximity to sensitive airspace, particularly on the east coast. The controllers will almost always offer an alternative deviation on the other side of the airway. I can only think of one or two occasions when I have been refused deviation in any direction. If you have no alternative but to deviate against the controller’s refusal then just transmit “PAN PAN, PAN PAN, PAN PAN”, stating that you are deviating due to thunderstorm. You will then hear the ATC supervisor come over the top to approve the deviation and to ask you to advise when clear of weather. It is never a problem and there will be no comebacks to you.