Last time I checked it was still possible to train ranged units and bring them down ony by one.
This strategy can work sometimes, but mostly, all you are doing is giving your enemy a chance to prepare (train more soldiers, get help from an ally, etc.).
Therefore, storming towers is necessary for many games.
I could use that argument for your example too, e.g.: Leather can work sometimes, but mostly, all you are doing is giving your enemy an advantage because iron units are much stronger and easy to get.
Therefore, iron is necessary for many games.
It's still a choice. And yes, you give the enemy more time, but you have more time as well to train more troops. If you're afraid the enemy will outproduce you, then you really need to consider sending all in.
