This is evidentally not going to be true for China as it will face off against possible heavily armored western tank for expeditionary warfare hence requiring advance capabilities. Plus what you said and what I said isn't in conflict as I said the FCS was never meant to produce a true MBT(Abrams successor) because as you said the US army didn't think there would be any future threats.
Well in hindisght its always easy to pick up on the mistakes. But back in the 90s if you would even suggest that China would one day rival or even surpass the US at anything they would just laugh in your face and send you to a mental hospital. That was the mentality back then, so US engaged in all sorts of colonial warfare everywhere with no thought given about overstretching, because again, at most they would be fighting people barely armed with rifles. They thought they could do whatever the f they wanted and that was that.
Type 99A is a design stemming from the weaker technological ages of China, no matter how people like to say it is highly modified and "westernised" compared to the original Type 99. It still uses old soviet AZ autoloader with no thought given to modern drone warfare and urban warfare. Also as I said advanced armor is still required to hold chokepoints and speerhead assaults etc even for expeditionary warfare which the 99A no longer suffices for. In fact I believe most equipment stemming from the age of "小步快跑" or catching up to western standards should be phased out of service or moved to second/third/training duty as soon as convenient. As the PLA is currently both financially and technologically capable of producing top of the line AFVs even compared to top western counterparts and hence should do so(as they are rumored to be doing already).
tl;dr I believe 99A is a product from a time where Chinese technological prowess have not reached world class level yet and hence not suitable for further major modifications due to compromises taken with the design.
This is the same mentality that got the US to exhaust its resources on useless programs. New toys just for the sake of new toys. And look at their situation now. They failed at every new AFV development program for the last 30 years or so, with the last one (M10) proving to be an absolute mess from the doctrinal and requirement point of view. So they end up with a platform thats inconvenient for any kind of practical use they could give it. The Chinese have been wise enough to just sit back, watch them fail and learn.
Because again, the 99A at most would be used against a country that is today the most important ally China has (it wasn´t all that clear at all 15 years ago, when the tank was in development), who by the way has and will retain the bulk of its military capabilities deployed literally on a different continent altogether.
On the other hand, the Chinese can look at the Russians literally squeezing all the value as they can from their limited budget and succesfully modernizing the T-72 platform in a way that is relatively very cheap and also reaching current top performing tank capabilities. There is no reason the Chinese can´t exploit the 99A platform growth/modernization potential to a similar extent.