A quick check - US has 3,300 combat planes, Russia 1,900, China 1,500, India 1,000, Egypt 900. I would guess these numbers would correspond with other military equipment like tanks.
Given your premise that 70% of our military planes need to be replaced would leave us with 900 planes still available. Do we really need 2,400 new planes? And how many of those other countries have outdated ;planes, too?
If we are to go down the path of isolationism, "America First", as Trump proposes and I agree with, and stop being the world's police force, we need to cut military expenses across the board.
Hey I get it. You work in the plane building industry. I have a retired brother who worked his entire life working for McDon Douglas, Boeing, and Saberliner.
The fact is, our military mega industry is more about business and jobs than it is about maintaining our military might in the world. Again, we spend more in military/defense than the next 12 countries combined. That is crazy for a country at peace and has a national debt that is going out of control.
But I guess that is future generations problem, just like the environment.