I disagree. In times of war would be when you need them most. And if they're stuck at the Tower they won't be doing much good. And it's not like they'll keep a Yellow on the frontlines. They'll be safe in the back, healing and throwing magic out when possible. It's possible they could never even be found by enemies.

I beleive it said in the books that a healer was worth a thousand men. Or maybe I'm quoting another series...I could be. Also, you didn't need to be very strong in the One Power to be a good Healer. Many of the best were actually very weak, sometimes barely even able to channel.