For simple reason T 90 deployment cost more and as for domination sorry to hurt your fragile ego but nothing in your arsenal is dominating T 90S
What an asinine statement. No disrespect to Russian tanks, but the T-90S is approaching 20 years out of date and you are seriously delusional if you believe that the PLA doesn't have better tanks in service. It's not all about the gun and armor that decides which tank is better, but yes the ZTZ-99A is almost certainly superior to that of T-90S also. FCS, battle management system, thermals sights, etc. are also better, simply because the T-90S is, as I said, beginning to show its age. Other non-tank equipment in PLA arsenal that will also are HJ-12 ATGMs, numerous types of UCAVs, barrages of 300/370mm rockets from PHL-03/16, salvos from AFT-10 missile carriers, etc. And that is even if your tanks can get sent to the front without running into mechanical failures. Remember when your team got disqualified from the 2017 Tank Biathlon because not one, but both of your T-90S tanks just suddenly broke down?
And yes of course the T-90S would win, at least on paper, in a head-on fight with a ZTQ-15 if you pretend that they are shooting at each other in completely flat terrain. But chances are that they will be facing ZTQ-15s in mountainous areas (the terrain that the ZTQ was designed to fight in), in which the hydro-pneumatic suspension and more advanced targeting systems would give it a significant or possibly even decisive advantage over the T-90S, especially when these areas are far from ideal for Soviet/Russian MBTs in general. You can go ask the Azeris (particularly their 4th Army Corps) how their T-90S tanks performed in a similar environment, and they were mostly facing ATGMs and RPGs, with occasional artillery strikes.
In any case, your T-90Ss are nowhere close to being as powerful as you portray them to be, or at least not anymore. And regarding that T-72 upgrade you keep stating as being equivalent to our best tanks, it just looks like one of those upgrade packages that the guys at UVZ scams you with if you are too poor to buy their T-90s or even T-72B3s. Even if you manage to complete the upgrade of 1000 T-72M1s to that standard within this decade, I doubt that they would surpass capabilities of even the ZTZ-96A, since its base armor is unchanged from the T-72M1 which was already bad for the 1990s.