As I know it, Russia just buys the electronics and installs them upon customer's request. For example, India had Shtora removed from their versions and wanted an Israeli AC for their T-90s.
The main problem I see with T-90 tanks are in the Protection/Attack capabilities. You can fire ATGMs with it but those ATGMs aren't exactly effective against MBTs. Russian APFSDS rounds aren't too great either. Protection wise, if you slapped on Heavy ERA onto the front of an Abrams for example you can achieve even more protection, but the T-90 is limited to only that much. I don't think Russia has plans on fitting DU onto T-90s so T-90 isn't too competitive. Hell, there's people in Russia who are calling for the end to the current domestic tank industry and for the Russian Ground Forces to only procure Leopards.
Protection wise, no one knows the official figures for the Type 99 so no one should guess. What we do know is that the Type 99's hull is based around the T-72's or T-80s. The Chinese have apparently copy and pasted Russian ERA so you can expect similar or degraded performance in that regard. However, the Type 99 is several tonnes heavier than the T-80 so one would expect a big more protection.
I don't think someone within Russia calling for the end of the indigenous tank program to be a valid judgment to the tank itself - I recall that there are those in the US asking for the stryker to replace the MBTs as well right?
Ultimately, if you slap K-5 on a Abrams, it will have insane protection. But the same can be said if the T90 employ Leo-2 technology like applique armor etc. Hell, I think you should be able to arm the T90 with a Rheinmetall 120mm L55 gun if you wanted to, but it is really besides the point. DU isn't that magical, Russia being the largest producer of Titanium could use it in their tank, heck, maybe even cast the entire tank in it as they have done with their Akulas.
According to:A Ballistic Evaluation of Ti-6Al-4V vs. Long Rod Penetrators, U.S. Army Research Laboratory, Weapons Technology Directorate; Using titanium alloy in armor will increase armor protection by around 60% with a 10% space detriment. The moral of the story is, nothing is set in stone and there are multiple ways of resolving an issue.
I am not sure if Russian ATGM are mediocre, if they are, why would the Israllies lose several Merkavas including the Mk. IV to Kornets? Which have a higher anti HEAT RHAe rating than lets say the M1A2 SEP? Surely, the Sniper and it's later variants might be a different weapon, but the technology is there.
I am not a Mahanist, I do not believe in huge armor clashes as much as I love them. They are too costly, too unpredictable. Why fight heavy tanks when you can out run them, cut their logistical supply and hit the support troop in the rear? A several T90 on a nato airfield will do much more damage than fighting Leos and Abrams?