Its a common misconception that Russia is keeping its best equipment in reserve and some how only used `old kit`.
They didnt.
T80BVM and T72B3 are both from 2013 , T90MS is 2018. This is literally their latest kit. According to some source T-14 production has stopped and T90 production has slowed, resulting in the modernisation programme of T72`s and reactivation of T64`s.
I've not seen anyone saying they are only using old kit. What people seem to be missing is the actual composition of what is being fielded. Very little initially was pulled out of Russia's maintained reserve stock, despite the claims, and they've been conservative in many cases fielding newer/regular active stock.
Hence for instance T-72 models which only exist in maintained reserve stock are only appearing now, BMPTs are only appearing now, etc.
Russian put several programs into place over the last few years to take older mothballed stock and reactivate it - this is generally separate stock to for instance the ~400-500 active T-80s and 3000 in reserve and make up a good percentage of the hardware used in this invasion and/or was sent to other regions so as to replace older active hardware to use for this invasion.
Point being people often band around that this war equates to, so far, Russia losing 1300-1400 of its pre-war ~2800 active tanks and 3000 of its ~13000 active armoured vehicles, etc. when it really isn't what is going on here.
It is a bit difficult to accurately compare how many of its soldier losses deplete from the pre-war ~900K active soldiers, but again people talk like this invasion has committed 200K men from that number and it really hasn't.
EDIT: This is further complicated by for instance it appears they've raided the reserve stock so as to reactive even older hardware in many cases and many of their elite guards divisions, etc. which were supposed to be at 80% standing readiness in reality were around 50% with often around 30% of their on paper numbers already committed to regions like Georgia, etc. so losses have had a big impact on their ability to function.
EDIT2: Was just reading reports that some Russian brigades have in some cases lost over 500 soldiers in 72 hours (out of a deployed strength of ~700 - 20-30% of their total size) - in comparison those brigades in brutal street fighting in Grozny lost 100-150 soldiers in several weeks of fighting...