You also need to watch out for the geopolitical issues before the war starts. Imagine that country A and country B are rivals, but each has its own internally divided politics with Fighters versus Peace-niks. In country A the Fighters bully the Peace-niks into accepting an increase in "defense" spending. Country B isn't deceived, and country B's Fighters try to persuade country B's Peace-niks to agree to more defense spending. Having succeeded they still have to decide how to split the money between tanks and static defenses.

The naive analysis just looks at the military effectiveness of the options. But there may be political implications. Perhaps if country B spends the money on tanks, that gets noticed in country A. That changes the politics in country A and lets the Fighters there persuade their own Peace-niks that more "defense" spending is needed. Whoops! The money that country B spends on tanks doesn't help defend country B as much as you would expect, if in unleashes counter-spending in country A.

What about country B spending the money on static defenses? That could help Peace-niks in country A push for cuts in country A's "defense" spending. That would multiply the effectiveness of country B's spending on static defenses.

I don't think it worked like that with the Maginot Line. Nevertheless, what a General says about military effectiveness misses part of the story.