Yeah, they don't. Like me, I don't need as much defense or atk as I need. But at the same time, it's still helpful. For example, when you battle ppl, and say your actual need of spirit is 150, but you have a max of 200, you only use up 150. So, you have 50 spirit left, which requires less time to regenerate, instead of waiting the full 150 minutes. It comes useful into events for sure, such as conquest ones.
Also, high defense tends to be a good bluff against ppl. The higher your defense max is, and you have a pretty good leader, but an actually low defense, all the ppl see are your level, leader, and max. So, they think you'd actually be pretty good, but you could actually be bluffing.
(and its not like you need that much health anyways...)