When Harry soulgazes Molly, he sees one potential for her as a warden. Molly has very little combat potential - that's made clear in all the books. Yet she has Finesse out the yingyang.
Being able to throw veils around, being able to make items/weapons, being able to prepare and use strategy. Enemy detection, obfuscation. Defense creation (I.e. wards). These are useful to the Wardens.
Wardens may be soldiers, but soldiers are more than just a hammer. You need recon and communications going with soldiers. Soldiers can occupy a location/civilian population. In peace time, or rather, when not firing weapons, the military has tasks to accomplish - peace keeping and public relations for instance.
Insuring Security can involve a lot of subtle things as well. You could have Wardens who function like the CIA: intel and counter-intel. Keeping tabs on the enemy from eavesdropping to breaking in and looking at their secrets. Sabotaging their operations. Removing the enemy's assets (either destroying their equipment, or removing pressure/neutralizing the people who help your enemy carry out missions). Feeding the enemy false information. As well as covering your own ass - plugging the leaks in your organization, monitoring your members to ensure loyalty, and protecting your assets.
For a spy, resorting to bullets often means you've messed up.
In these cases, you want those with fat Thaumaturgy, veils, wits, social skills, and just enough Evocation to get themselves out of danger.