I keep thinking it'd be nice if troops were somewhat easier to maintain because the flash approach feels too much like a twitch strategy (not good planning, just fast timing).
I guess I feel like you should be able to make some preparations for future attacks without needing to be on constant high alert to flash troops as needed so you can avoid excess and sudden resource drain. As is, a modest nation that makes a sufficient defense will really open itself up for a second strike from a strong nation due to the cost of a single defense.
So, what if you could have reserve/active troops? Active troops would have the same cost as they do right now per war tick (12 hrs), whereas passive troops would not be considered defending but incur a per tick bit cost. If it's still a balance issue, perhaps there could some kind of activation cost so that there's a minor penalty for switching them to active.
Not sure how that would all work, it just feels like rich nations have an outsize power advantage which leads to the impression, when they attack, that they are toying with you rather than making a serious bid to create an empire.