Another way to look at it is the ying-yang principle - being aware of balance.
If your German opponent is buying all expensive units, like mech infantry, armor, and bombers, then what do they not have? Lots of cheap infantry.
What can the Allies do then to counter that? Create the structures needed to get lots of cheap infantry into the middle of the board. 5 armor and a couple aircraft are an expensive way to kill a stack of 10 infantry :-D
Is your opponent going north with all their expensive mech units? Be strong south. They go south? Be strong north. Stretch them out. They aren’t defending the flanks with their headlong strike toward Moscow? Attack the flanks. Not building enough navy and fighters? Set up a navy-killing structure in the Atlantic.