Russia is a continental power all invasion comes through land mass.
uSA and UK are naval power they project force outside their sphere of influence.
Their strategy reflect weapon design. India is a unique case having been invaded by hordes of barbarians on western front and also by british.
Come what you say our adversaries are fielding tanks in thousands you will need tanks to fight them.unless you plan to use tactical nukes
Russian are not any kind of power any more
They just legacy of there Coldwar legacy
In modern era economy also matter and numbers of allies
By end this decade even india will surpass them in terms technologies
In many areas we already did
Today in modern warfare air power dominates by land
Like said field thousand tanks doesn't make them
Any stronger if your Edge in air power and Fire power
A Single CBU-105 or Barrage of Smerch is enough to counter batalllion of MBT's
Modern Sensor fused Munitions and rocket propelled Systems gives you Advantage in fore power
If take stand off it is over kill.
Today in modern warfare having huge military is a logistical nightmare it only trains your funds
Like Case of India 40 % of our budget drains in Salaries and Renumarations
OK let's take into account experience of
Latest conventional war
Which was
Us invasion of Iraq
Look at how many forces US
pitted
3 lakh against 1.3 million
And Iraq has huge amount soviet style equipments
That doesn't saved them from anahilatikn
The massive use of Air power and Calculated
Strikes made them March into Bagdad in just 4-5 days
en.m.wikipedia.org