The T-90 is "very survivable." That's a sentence just BEGGING for some Clintonian parsing...what does it MEAN, exactly?
The "top attack" issue isn't going to go away anytime soon, because main gun rounds are going to be using it. That means a LOT of armor on the roof, and that stuff gets HEAVY.
Again, it is heavy but the T90 is 45 tons with an over powered power plant, it can easily carry the extra weight of top down armor. No reason to stop a tank. These arguments were around when ever a new weapons system comes out and they've all been proven wrong. One of the Popes once said when he saw the crossbow in action that such a terrible weapon would surely end war.