I have 2 maxed/CDed bronze soldiers I use for anti-zerg. I don't keep them in the team but sub them in when required. Instead I have a Ninja as they are versatile. A bronze Ninja at level 40 can be handy for a few things - anti-zerg included.

On my original account I had a maxed/CRed Phyllis (no CC so only 6 to deploy) who was handy but really not worth the loss of so many soldiers to make. Unless you are overflowing with spare soldiers they are better kept for CCing.

Also worth noting a Mage's range is only to the target they shoot. The splash can hit anything within range of the splash, thereby extending the range for taking out a swarm. More splash = even more extended range.

Personally I'd go with what people have suggested here. They know their stuff.