But yet, there are only around 550 T-90’s in Russian military service. Does this mean the Russian Army wants to buy large quantities of the T-14 Armata instead?
The T-90 was an interim proof of concept step from the experimental T-80.
The T-14 Armata is set to become the Russian main battle tank of the future - along with the economies of scale by using the same platform for many other tracked combat vehicles. (https://en.wikipedia.org/wiki/Armata_Universal_Combat_Platform)
Here’s a better comparison of the T90 vs MIA2 variants:
http://nationalinterest.org/blog/the-buzz/russias-armata-t-14-tank-vs-americas-m-1-abrams-who-wins-13825