Russia has manufactured its own security concerns, though.
Putin doesn't have to view NATO as a threat: he chose to.
NATO was literally formed as a military alliance for the specific purpose of countering Soviet expansionism, and when the Cold War ended it was not terminated, but rather its mission extended. No kidding, he views NATO as a threat, because it still is. Do you think the United States would feel differently if the Mexican government was overthrown and a Russian-friendly government installed, and in the span of five years was considering entry into CSTO?
It's not like a scenario close enough for comparison happened almost exactly sixty years ago...does anyone else remember the time the United States deployed nuclear missiles in Turkey?
He chose to because he has an imperialist dream of Russia being a great player again, and NATO threatens its ability to exercise that imperialist design over its neighbours, and because liberalism and democracy threatened his grip on power and the ability of him and his cronies to extract billions from their country into their own pockets.
...yeah?
MBTs still have their use...
Not really. We need to remember MBT's are a specific type of AFV, designed to fulfill a specific battlefield role in pursuance to specific doctrinal needs. That being, rapid, armored, direct fire support for infantry and mechanized infantry in medium- to large-scale, high-intensity, conflicts which feature combined arms. The issue is, that's a role for which MBT's are ill-suited for in an era marked by low-intensity and asymmetrical conflict, in which belligerent forces are decentralized or decentralizing, and mass psychological warfare has taken the forefront over direct conflict (i.e. fourth-generation warfare).
The question isn't whether MBT's are useful, but if they're cost-effective, and if there are alternatives better suited for the contemporary battlefield. That's not just a question of price of procurement, that's the price of deployment and the price of supporting the unit logistically in operation -- armament, fuel, supplies for vehicle and crew, labor hours and facilities to maintain, and the like although I'm pretty certain I covered the main points. That's not a price that can be taken lightly, when contemporary conflicts are marked by asymmetric attacks on supply lines and columns in-transit, and when objectives are more often than not urban cores in which MBT's strengths cannot be adequately leveraged while their weaknesses easily exploited by opposition forces.
This is a development we've seen before in the history of mechanized warfare. Early Cold War MBT's/UT's, primarily those designed before the advent of composite armor, shared more in common with WWII self-propelled artillery and TD's than they did comparable mediums, heavies, or infantry tanks (depending upon which country we're discussing, and their doctrines) simply because ordnance development so rapidly outpaced armor development, that no sensible tank armor could resist incoming fire. The German Leopard I is, more or less, the apex of this era, considering its devastating speed and armament, yet at the same time being less armored than even WWII-era recon vehicles -- and the contrast between it and its successor not a decade later, Leopard II, no clearer.
Even in the Soviet military, is this demonstrated no better than the short operational life of the IS-8/T-10 and rapid replacement by the T-54/55, because while the former was one of the most fearsome tanks ever designed for its time, it was cost-ineffective and poorly-suited to the rapidly-developing battlefield.
...but using old cold war era tanks like T-72s just won't cut it on modern battlefield.
Obsolete tanks' vulnerabilities to the almighty Toyota pickup notwithstanding, most militaries in the world still use Cold War-era tanks. Hell, some still use WWII-era tanks. They're either what those countries can afford, or those countries lack the technological or industrial bases to procure better.
...T-14 Armatas it would be completely different story...
T-14 was a fairly respectable concept, until NPO's took a good, hard, look at the F-35 and decided they wanted their own inordinately expensive modular multi-role boondoggle. Again, it comes down to cost-effectiveness and what's best-fit to doctrine. Unlike the US, Russia shares land borders with most of its expected belligerents, and therefore has little need to stack every single force multiplier it can leverage into as small a fighting force as possible, to minimize the logistic burden of that force.
And -- I alluded to this earlier citing Russia's failed rapid dominance strategy -- if Russia wants a successful military, it needs to go back to developing and relying upon its own doctrines, opposed to emulating Western doctrines it's ill-suited to emulate. The trend of Russia failing militarily when it attempts to emulate the West, but succeeding when it develops and stands on doctrine that plays to its strengths and weaknesses, isn't a new trend -- it goes back
at least as far as the Napoleonic wars.