A point to consider, military constructions and developments have - historically - resulted in the development of means to counter them. In a purer sense, it's dangerous to put all of your eggs in one basket, even a very safe basket, because somewhere there's a problem solver able to devise a method of defeating your basket's defenses, and before you have time to develop a new defense, your basket's been penetrated and all your eggs absconded with.
Historical/allegorical/literary examples?
- Troy - Trojan Horse.
- The Maginot Line - Belgium.
- The Whole Egyptian Army - Paint Cats on your shields.
- 13 Ships Hopelessly Outnumbered by the Japanese Navy - Abuse superior usage of terrain to force a drawn out engagement accentuating the advantages of your superior vessels, resulting in a Japanese rout and a flawless victory.
- The Death Star - Sabotage
- Scientists Have Revived Modified Dinosaurs Which Pose An Existential Threat to The State of Costa Rica On a Small Island Off the Coast - Burn it down, burn the whole thing down.
The point is, you probably can't build a thing so impressive, dangerous, or resilient that someone else can't invent a creative way of destroying it with a little lateral thinking; this sometimes applies to entire armies, but it's much easier to recover from this kind of thing when your entire military isn't a single massive vessel (or a few of them) - every problem has a solution, redundancy is the same as flexibility here, and is therefore your friend.