An infiltrator who intends do have a meaningful impact needs to do more than just deal lots of damage. You need to do the right damage, at the right time, to the right people. When you get it right, a single knife thrust can do more damage to a realm than burning every bushel of food in it.
Just ask Ohnar West.
Meh, Ohnar West still has 4 duchies, so I consider they are doing pretty good. Whatever was done to them obviously wasn't meaningful enough to send them spiraling down.
Burning food is quite another story. If you have an army looting the food stocks, and then you send a few infiltrators after those regions where they are hiding all the rest of the food from your troops, you can effectively deal the crippling blow to a realm that might have otherwise had enough reserves to last quite a while.
Assaults are not an infil's best option. It's risky, it's success rate is low, and it's use limited to very exceptional scenarios. Sabotage is much stronger.
